I'm going looking at a P38 2.5 DSE AUTO on an S plate 1998. Any advice as to what I should be looking out for. My current vehicles are a defender 110 and 90 plus a series 3, so I know a bit about Land Rovers. But don't know much on Range Rovers. Any tips would be appreciated.

Money pit if you don't do your own maintenance, other than that, get a nanocom, it'll save you time and time again.
Common faults on the diesel are hot start issues, which there is a fudge fix for or get the timing/fip sorted.
Blend motors and matrix on the heater are common failures and quite a big job (check for wet carpets and check you can divert the air manually)
Air suspension can be problematic but not complex to fix generally.
Sagging headlining is common.
Lots of other things can and do go wrong but if you're handy with the spanners, most things are well documented and relatively easy to fix.
Wammers is the guru on the oil burners, there's not a single problem he can't suggest the fix for!

As above plus RF receiver, tired lift-pump / FIP, timing chain stretch. If someone can get diag on it then do so. Will need specialist diag like Nanocom.

I agree completely with the two posts above. You will NEED Nanocom - if it can't be part of your purchase/budget, I'd walk away.

I'd be making sure its still on air, and not been butchered in any other way. Ideally take someone with a P38 with you.

Check all windows and sunroof work as switch pack can be a pain.
All heights on air.
ABS light goes out.
Viscous fan can fail.
leci seats.
absolutly no faults on message centre.
Drive in high and low range.
Starts on the button every time.
Central locking and lazy lock.
Basically Every thing.
Best of luck.

Budget £1000 on top for all the things that are going to need replacing in the first year. It WILL break! After that it should settle down ... he says waiting for the parts to arrive with a big red metal brick on his drive!