I've had loads of these. That particular year model is fondly known as the XJ40 saloon and the early cars were notorious for problems. The 3.2 feels a little lethargic compared to the 4.0L unit.
Check for :
Rust on inner wings, near suspension tops (MOT failure, but repaireable)
Rust on bulkhead
Rust on boot lid
Rust around sunroof (if fitted)
Diff wear (whine or excessive noise from diff)
SLS (self-levelling suspension) - most quickly broke and were retrofitted with standard suspension.
General electrical gremlins
Lighting electronic control modules, front and rear.
Air conditioning leaks (in-dash evaporator especially difficult to replace)
Front discs warped
Broken/failed door handles.
Lots of other things I can't think of right now but these are the main things.