I fear that will remain one of life's mysteries.

 

I spent another afternoon on trying to resolve this recently, but was only able to proves negatives rather than any useful positives!

I first reprogrammed both XK8 fobs to my X type and proved they operate correctly at a goodly distance and then programmed the X type fobs to the XK8 only to find that in that scenario that they had as short a range as the original fobs. So I think that proves that the fobs are not the cause of my v short range.

Next, removed the SLM, opened it up and re-soldered all those connections on the small receiver circuit board that its practical to do. Re-furbished the contact points at the ends of the tape connection between the two circuit boards and checked all connections between the circuit board and the antenna on the rear screen. No improvement in range!
Tried a new, 433mHz antenna with a new coax cable and when that had no effect, tried an antenna signal amplifier to see if a boosted signal would help. Another failure!
I think my only option left is to fit a different SLM, but the drawback with that is that for some inexplicable reason (maybe supply and demand?) is that the version for the late models, ie MY2005, the going price in UK is anything from £500 up. That's just not good enough value for money to my mind for a few extra yards of range.

So unless a circuit board repair solution is found it looks like I'll continue living with it

 

Thank you for the detailed reply. My car is supposed to go in for a couple of items in the coming weeks. Intend was to let them have a look, but based on what you all described, and having read most posts and done other searches, it seems to be coming down to that module in question. Hence little sense to let a garage for £100 per hour do much searching vs getting the module professionally repaired. Have you tried Jag Berkshire that charges about £220 for your repair? I