Head gaskets have been known to be a problem. Check the usual things, although the TD5 is quite capable of losing coolant *without* a head gasket failure, so if the coolant level drops, it's not necessarily a major problem.
Does it have ACE? To check, either look for a hydraulic ram connected to the anti-roll bar in the front RHS wheel arch, or mash it round a corner and see if it rolls or not. You may be able to hear a whine which changes in pitch with the engine - this is the ACE pump. It's normally audible, but if it's loud it could be on the way out. The ACE hydraulic pipes can burst, which can be pricey, so check it's had all its recalls done!
As it's a seven seater, it will have air springs at the back. The pump (which will cut in whenever it self-levels, such as sitting at traffic lights, etc) should again be slightly audible, but not loud. If it settles overnight it could be leaking somewhere, but the air suspension on the TD5 is generally quite reasonable, not quite so quirky as on the P38.
Apart from these things, everything should be fine and dandy. Good choice!
