How difficult is it to get to the pump, hoses and bladder to check where a leak might be hiding?

It pumps up, but in a minute or two has completely deflated.

Scale of difficulty
1. "Look here"
10. Can only be done with Whitworth wrenches and the engine and transmission out while the top exactly 23" from being latched.

 

From what has been posted on here before, it is the connection/clamp between the supply hose and the bladder that leaks out. From memory, folks have been able to fix this without requiring new parts.

To my knowledge, this is accessed from the back of the seat back. The "skin" has to be unhooked from the bottom and rolled up. You might want to search for the headrest repair as it calls for the same procedure.

 

Yes, getting to the Lumbar can be a bear. The back of the seat has to come off, and they use these little trick metal clips to hold the leather to the seat back.

Here's at least one post that might be of help putting it back together:
https://www.jaguarforums.com/forum/x...covers-157762/