Many/most of the problems are minor electrical ones, though as the one you're looking at is a Series II these are not usually as bad as they were on the Series I.
A thorough check of everything electrical is a good idea though, e.g. electric windows, sun-roof, mirror motors, etc.
Obviously also a look at and listen to the hydraulics is a good idea, does the pump run frequently and/or does the valve tick frequently? Does the car pump itself up quickly? In fact, being a Series II it should have an 'anti-sink' valve so it should stay up overnight.
If reasonably well cared for the engine will go a lot further than this. The real problem with automatic XMs is the gearbox, these are reputed to last only about 100k/120k. If (and only if) the auto oil is replaced frequently and religiously they will last longer. Since it's actually impossible to replace the oil this is rarely done! (The way to do it apparently is to replace a little every few thousand miles to keep it reasonably clean, I don't have an auto).
Not scintillating but OK.
Pretty good for such a big car.
Come and join the XM list, snipped-for-privacy@yahoogroups.com and you will find lots of owners who know more about the 2.1 auto than I do (I have two
2.5TDs).
My son who is 6'6" fits in the XMs OK.