Plastic! Can't live with it and... well...
Plastic was again the reason for another problem as plastic just loves to break - even if it is not located in the hot engine compartment.
So the initial issue was that it was no longer possible to open the passenger door via remote. This issue just started before I bought that car a couple of month ago. I then sprayed WD40 and later silicone spray into the mechanism and this seems to have solved the issue - but not really, as the remote worked not sometimes and sometimes not. And if not, I had to pull the locking lever inside.
But suddenly it got worse: the inside levers somehow jammed - I could no longer pull them nor retract them - and...: it was no longer possible to lock the door (neither with the remote).
To remove the door locking mechanism, I removed the door trim (after removing those 3 screws), all the foam which was on the inner of the trim just fell off in the shape of dust. I knew already that it is pretty much impossible to pull the trim off without damaging some of those plastic fasteners, but I have them here anyway in reserve (cheap to buy on Aliexpress).

Part Numbers:
So I removed the mechanism. My 2004 2.5L RHD had on the passenger side the mechanism with the P/N 1X43-219A45-CL. The last letter always stands for the revision-version. So I had the L. According to an ebay listing, CL, CR and CN are interchangeable. In my search for a replacement part I also came across the P/N 1X4A-F21813-BE, which looks the same to me, but I can't say, if it is interchangeable. And I also came across, what I thought, should exist: The Ford Mondeo mechanism, which apparently is interchangeable: 1X4A-F21813-CE. Ah! So the part I came across before (1X4A-F21813-BE) is the Mondeo version. And Mondeo fits in the X-Type. But I do not know, if BE would fit, because the first of the last 2 letters (here B) always describes a difference application - like the difference between driver's door or passenger door...

I contacted a lot of wreckers today (in Australia), who would normally have X-Types. Nothing. Yesterday I tried already to open the mechanism to check, if I can fix it. But I could not open it. Other than that I noticed immediately that there was a little bit of plastic broken off in the outside. Fired up with desperation (as no wrecker had that part) I gave it another go, if I really can't open the mechanism. I did it! And I fixed it. I did 2 things:

Cleaning of connector pins:
I had most probably corroded connector pins - and if that was not the case, cleaning them does not hurt:
Cleaning the contacts of both connectors with a new wire brush (with undamaged wires, so that they can go into the connectors) and using WD40 or equivalent (I use Boston).

The broken plastic bit:
And the other fix - regarding the broken plastic, was more complicated and needs a lot of pictures to explain, incl. of how I opened the mechanism. It might well be that this broken plastic is normally the issue, when one of those parts fails (which seems to happen often, as all those used parts are sold out), which again means, you could have fixed your mechanism rather then buying another one, which will also fail after a while...:


Detail of the broken plastic bit. Explanations to follow...


That is the upper half removed from the base. There are plenty of clips and latches, which all want to be opened, but that would not suffice. 3 metal latches (No. 5s) need to be bent open. Note No. 1...: it sits in No. 2 (see next picture).


Opening and closing the door leads to No. 1 moving No. 2 to the left and to the right. This again turns No. 3 90° to one direction and back. That was design intend. However, as a little bit of plastic, which would have restricted the 90° turn, had broken off (see last 2 pictures). No. 3 could now turn a bit more than 90°. No.3 "operates" the micro switch in the next picture, which is mounted on the other half of the mechanism.


This is the before mentioned microswitch.


So, depending on if the door is open or closed, the are normally 2 positions possible: Position 3a...


...and position 3b.


But this is the third position (3c), which should not have been possible as the plastic lever (which however broke off) would have restricted a turn of more than 90°. Thus, this is a position, which is "not possible" and the micro-switch "reads" an impossible situation, which would have confused the whole system! Hence those failures, where the remote would not open the passenger door... I needed to open the mechanism to be able to understand it. I found my own way to fix this. Obviously any attempt to "fix" the broken bit of plastic by trying to add a bit of plastic (heat glue or otherwise), but not last for 3 seconds... Hence, I come up with something else: Look again at the second picture from the top: Just to the right of No.1 I added 2 tiny bits of rubber (2mm thickness each). I glued them into position with shoe-glue (Al Bundy could have told you that on his shoe-hot line 555-SHOE... I actually did it again after taking this picture and it looks a lot neater now, too. This modification serves as a new stop to avoid turns of more than 90°.


Here are the 3 metal latches, which need to be bend back before you can take the mechanism apart, if you want. Maybe you don't have to, if you manage to glue the new "rubber stop" into position without taking the mechanism apart. I actually had to take it apart twice, as I forgot the first time 'round to re-position the micro-switch, which hangs on the second connector (see below picture with No. 6). I also had that rubber removed, which is missing here in the picture and glued it then back on. But if you want to avoid taking the mechanism apart you need to find a way to insert the rubber stop somehow into position despite that big metal part now being a bit in the way (as above).


Detail of 2 of the 3 latches, which need to be bent to open the mechanism. Btw.: Opening the 3 bolts on the mechanism did not do anything for me.


That is also a tricky one: If you want to take this connector off, the "latch" (No.6) needs to be bend back momentarily.


And luckily I figured this one out quickly when removing the mechanism from the car: the white part needs to be pulled out (using a very small screwdriver as aid, or even just with fingers) to release the metal rod, which connects to the outer door-latch.


Detail.


Detail with metal rod. With the white bit pulled out, it is possible to re-insert the rod sideways, which makes re-inserting after mounting the mechanisms in the door already (with those 3 bolts) possible.


And this red cable goes to the interior door handle.

So it works again - and I did not have to buy a new door lock mechanism. After having contacted so many people about that part, I have received one replay on facebook, where somebody scraps his X-Type (2002, 2.5L), and he used a Ford Mondeo mechanism in there (as I wrote above: 1X4A-F21813-CE). I replied to him that I managed to fix my part meanwhile, but I still may buy his mechanism, if the price is right (to have 1 in reserve), but I have not heard back yet... Maybe he was serious when he wrote pick up and he does not mail at all...

"A few" PSs, which came to me over night:

PS1: I described above in detail, how No. 3 probably causes a wrong "reading" on the micro-switch (which is not seen in that pictures, as it is part of the other half of the mechanism), when it over-rotates the 90°. I wanted to add, that this is not the only microswitch operated by this rotation, as I can hear the click of a microswitch when moving No. 1. So I need to add that it is important not to add 2 "full length" little rubber bits of 2mm thickness, as this would prevent the lever No. 1 to reach its designated position prematurely and cause some other fault. Note that the other rubber bit I added is only half length (see picture above).
That other microswitch (which I can hear) is inside of that half, which can possibly be opened buy removing first those 3 bolts and opening those 2 latches. But what the trick thereafter is to be applied to actually open it, I could not figure out, but luckily I did not have to open it...

PS2: Btw.: I did check all my microswitches for continuity with a multimeter on the connector pins. Search for a while and you will figure, which pin is which.

PS3: If you do have a choice, pull the interior trim off the door when it is as warm as possible outside. Because, here we have that old issue again: Plastic! (See top of this thread). A number of those fasters will break, but also a few plastic bits of the backside of the trim will break off. Luckily there are no beauty-contests for how the back of the trim looks - I re-positioned all the broken off bits of the door trim inside with black roof and gutter silicone. If it is warmer, when you pull the trim off, less plastic will break.

PS4: I cleaned off both sides of the trim with a water pressure cleaner and used Gumption (a really good Australian household kitchen surface cleaner) and then liquid laundry detergent, both times using a dish washing brush. Remove the tweeter (simply remove by turning - easier than removing its connector anyway) and best remove the window switch as well. I will - before reinstalling the trim - place some packaging material (thin foam) onto the backside to replace the former foam-layer, which was reduced to sticky dust over the years...

PS5: If your problem with the door-lock-system is that you can pull the interior handle(s), i.e. they are not stuck, but they have movement), but nothing happens (i.e. the door does not open), I would suggest that that plastic part, which is partially broken my my mechanism has now totally broken off. Maybe it is possible to attach the cable from the interior handle in another way as a remedy. But keep in mind that the cylinder-shaped end bit needs to be able to rotate freely in that new design as well.

PS6: If you where wondering about the gray rubber insert next to the red cable end: That has nothing to do with the original system of limiting the turn of No. 3 to no more than 90°. That is simply a blanc stopper, as there would be different applications of that door-lock-mechanism, where the red cable end goes where the blanc is now, and the blanc would then be where the red cable end is now. But not on the passenger front side on my car - different application - maybe on the driver's side - I have not checked that...

PS7: I totally forgot to mention that:
After understanding the trick of having to bend back the No. 5 edges, there is still one major problem to get the two halves apart:

So after having bend back the 3 metal latches (No. 5s) and having made sure that the four No. 8 latches are bent open, the two halves are still stuck together, because there is kind of a strong bond at point No. 9. To overcome/loosen this, I pried in with a flathead screwdriver at the gap No. 10, using the screwdriver as lever between the plastic housing from the inside and the metal part underneath... And to get those two stubborn parts back together at reassembly, I used a pair of plumbers pliers to press them back together carefully (remember: I did all that twice, as I forgot to reinsert the microswitch of the separate connector the first time around...

PS8: About the part numbers again: As you can see in picture above, my P/N is 1X43-219A45-CL. How to understand those Ford/Jaguar specific P/Ns: 1X43 is the prefix and means: X400/X-Type. Base number 219A45 says it's a door lock mechanism. The suffix can have 2 and rarely even 3 or 4 characters (the third/forth ones are a colour code for parts, where this is important - if such a part has only received a base coating and has no dedicated colour jet, this character will be a "W". But this does not apply here. The second character of the suffix is the revision level. It starts with "A" and each improvement on the original design get the next letter in the alphabet. So this is why I found e.g. an ebay listing, which described the part at hand as CL, CN and CR at the same time, as some revision levels are upward and downward compatible. The first character of the suffix is the specific application. For example the light switch would have a lot of different letters there - all describing different light switches for different markets and different specs. Those parts with different first letters of the suffix are not interchangeable. Obvious, for which variation each letter of the alphabet stands for at this first character of the suffix differs from car-model to car model, and according to the marketplace offer I had for the Ford Mondeo door lock mechanism, apparently 1X4A-F21813-CE fits my RHD X-Type at the frt. left side. Thus, coincidentally Mondeo also uses "C" for the RHD left passenger front side door lock mechanism (unless I underestimated the complexity of this numbering system and "C" says across all models: RHD left front mechanism). And to complete this tutorial of the Ford P/N system: 1X4A stands for Mondeo and F21813 is the base number Mondeo uses for the door lock mechanisms. Now you know as much about Ford P/Ns as I did after working the first few weeks for Ford in Cologne cataloguing Motorcraft part numbers...

PS9: When looking at ebay listing for a replacement mechanism I saw at least on one pictures the first cracks in the plastic, where my part broke as well - I guess you can see that only, when you know what to look for and I do not think that the seller was even aware of it - that is the downside to using plastic in production, the downside to buying second hand plastic parts and it is a big problem, when they stop producing new plastic parts to replace the old ones, which self-destruct "by design" with age - all in line with the vehicle manufacturer's code (which they live by apparently) that a car has exceeded it's expected design-lifespan after a certain number of years - and this is probably after close to 10 years, judging by the ATF (Automatic Transmission Fluid) in the X-Type, which is officially in there "for life", which is obviously utter nonsense, as the transmission manufacturers would confirm...

PS10: To remove the foam, which sticks to the sheet metal of the door (not the foam, which WAS attached to the backside of the trim, which would have disintegrated into dust) use a heat gun to temporarily soften the glue there. Heat up again with a heat gun when re-attaching. I mention this, as there seem to be a lot of people,. who do not know that, as I can see on the torn foam on the cars, which I bought...)