This is VERY helpful, thank you all!

A few points that I'm thinking about after reading these replies:

1. The High Gearbox Temp warning light has never lit up during any of this. This fact is one of the reasons why I never really considered the cooling circuit as a potential culprit (until now). I don't know what the trigger point is, but you'd think that fluid temperature of 240-250* would light that sucker up like a Christmas tree! The light could be burned out or something, I guess.

2. The flow test mentioned above is just what I was looking for, and that's how I will proceed for now. I do not (yet) know what normal flow is, but if it's zero or just a tiny squirt, then we're probably on to something. I will figure out a way to do this and I'll report what I find. I am going to educate myself a little more before I dig into the project.

3. I'm not yet educated enough to know how vital the cooling circuit is to keeping the operating temp within range. I would THINK that it needs a way to dissipate excess heat, especially on a hot day, which is the only time this problem arises.

4. Maybe I have a cheap knockoff dipstick that doesn't have the proper shoulder, and is giving me false readings. I have measured the graduations on my dipstick over the years in an effort to double check, but I will reconsider this, because I understand how vital the fluid level is for this transmission. Maybe I need to find a different, better quality dipstick. Maybe the shoulder isn't big enough. Idk.

5. If the transmission is generating excess heat due to a failure of some kind, then two things have to be true: (1) the shop that rebuilt my transmission did not actually do the work, but left my car sitting in their shop for a month untouched because this problem was active before and after the rebuild; (2) I am unable to tell if the transmission is slipping. I would think if it has been slipping all these years, and the shop did not rebuild it, then a catastrophic failure would have happened long ago, or at the very least, detectable slipping would be evident by now. It shifts perfectly all the time, except when this problem occurs - after a long drive on a hot day, followed by driving in start/stop traffic. I'm not quite prepared to believe either of those things just yet, but as I keep saying, everything is on the table.

6. I'll check the cooling circuit first, and HOPE that it's blocked, because then we're probably on to something.

Thanks again. No idea or suggestion is too silly, so keep them coming. EVERY idea is on the table. As I've said before, it has become a quest!

 

Yea, it's been a while, but since I've been idled for a while with a total knee replacement and the virus, I got back into reading through the forum. I've also been gathering parts for some much needed work on the ride; whenever I can roll around on the garage floor again.

 

The attached document is for Mercedes.

I follow the instructions in the Jaguar service manual:

 

M. Stojanovic, you are correct. I should have clarified that the MB tool will not hit the pan.