Could it be a bad pressure solenoid? Or would a bad pressure solenoid always cause a problem, not just when its warmed up (logical thought process)?

I'll add to what Phil said, I picked up my X and it did the same thing as OP. That Bearing wore killing the O ring. The rebuild is really not that bad. It took me a couple weeks, but that was just because I had to wait on shipping for the 3 metal pipes and a new b piston ( I dropped it and chipped the edge of it off).

Well then, it looks like its rebuild time. Oh joy!

I've been looking at rebuild kits/options. I noticed a lot of kits include an "updated" A-Drum...while others include a "heavy duty" Kuhle A-Drum.

Do you guys have any info on this? Should I replace mine with an "updated" version or the Kuhle heavy-duty one?

I will be using the X5 to haul a 21ft boat every so often. I'd like to have the tranny last for another 50k at least.

It depends whether you have an early model or not. Can you crawl underneath and read off the serial number of your transmission?

http://i260.photobucket.com/albums/i...ps419bf15e.jpg

http://i260.photobucket.com/albums/i...psa16eca2b.jpg

Phil

You can connect a pressure gauge and see if it is holding pressure. If it is not holding pressure time for a rebuild.

https://www.youtube.com/watch?v=13G-sGMvulk

This is why you should replace the A drum when you have it all apart.

https://www.youtube.com/watch?v=UpG91-ZzYY8

How do you connect a pressure gauge to it?

I'm going to try to crawl under it tonight and let you know what I find.
Which serial numbers were the early models?

If you don't know where or how or have the equipment and facility to connect a pressure gauge to the trans I suggest you take it in to a reputable repair facility and paid to have this service perform.

I would much rather learn on my own, and invest in the necessary equipment. Just looking for a brief "tutorial" since I have never encountered a situation where it was necessary to run a pressure gauge to the transmission/solenoids.

If the serial number is greater than 355862 then your transmission is fitted with the stiffened A-clutch drum :

http://i260.photobucket.com/albums/i.../LaterDrum.jpg

and has the upgraded hydraulics to eliminate the pressure spikes (10mm rather than 9mm wide main pressure valve spool land)

http://i260.photobucket.com/albums/i...psce1fbadf.jpg

which caused the A-clutch drum failures around the retaining ring groove

http://i260.photobucket.com/albums/i...reofgroove.jpg

Phil