FWIW, I've never seen more than one drain plug on a Jag diff.

The filler plug is biased towards the right and about 2/3 of the way up on the rear cover. It might be hidden under dirt. The diff can be filled from below. No need to fill thru the trunk.


Cheers
DD

 

When I first acquired my car (86 XJ6) a couple months ago, I crawled under it to examine the differential. The fill plug is exactly where Doug stated it is. It takes a contortionist to reach up there and unscrew the plug (which has a square end on it). I was able to do it by reaching up over the rear end with my left hand and using a small adjustable wrench. Slowly, I turned the plug a couple threads at at time until it came out. The first turn was difficult because it had not been taken off in eons. Once it was off, I dipped my finger in the hole to check the level of fluid. It was right up to the bottom of the fill plug. Cleaned up the threads, put some anti-seize on it and put it back on. I will be changing the fluid once I get it on a friends lift. That will make the job much easier.

A general rule of thumb... never take off the drain plug of a differential, transfer case, etc unless you are certain you get the fill plug off first. That way you are not left with one that is empty and renders the car unusable.

 

I'd change lube shops too.