Make sure it has had it's timing belt and tensioners replaced, ideally within the last 20k miles or so. Also, it should have either had it's original engine changed for one with a steel lining or the original Nikasil lined block rebuilt with steel linings. Look to see if it has had a blow-by test performed, this is the standard test for Nikasil bore issues with the old Jag V8s ...to be perfectly honest having done 130k miles I can't believe it would still be running if it hadn't had the problem sorted a long time ago, so it'll probably be fine. But do watch the timing belt and tensioners, that's some preventative maintenance you want to stay on-top of with these cars.
Other than that, make sure everything works, check the aircon blows cold and that the heater blows hot, heaters can be a failure point on these, check the autobox shifts smoothly and quickly and check carefully around the arches and basically where ever panels meet for rust. Other than that, they are pretty solid cars. Oh, the history is imporant, history and condition are more important than mileage on a car like this.
You probably know this stuff already, but I feel better having given you a quick brief anyway, do some research on these older Jags though, so you know what to expect. I think they can be terrific bargains if you buy carefully, especially the XJR, but, they can be very costly if you don't do it right. I'm really not sure about the one in the advert though, it's just 'too' cheap really, I'd be quite sceptical myself.
