As long as it has been maintained, they are very longlived vehicles....
The BMW M51 I6 Diesel is a strong and reliable unit, as long as it hasn't overheated as the heads crack quite readily in this case. The Radiators are a bit of a weak point with the top baffle inside being crucial to correct water flow through it...this baffle does tend to work loose!
FIP timing issues can cause hot start problems, but is easily solved by FIP timing adjustment, new chains or the workaround which is to fit a box of tricks to fool the ECU into thinking the engine is cold and not hot for 30 seconds during the start process!
As with all air sprung vehicles, the air bladders have a design life of 7/8 years so check these for signs of replacement or if they need replacing, negotiate on purchase price. A tired compressor feeding and air bladder leak will fail eventually, but the refurb kit for both the pump and the air valve block are cheap enough and easy to fit!
P38's rarely suffer rust and are considered the most rust proof Land Rover product made, which is quite a claim!!!
Electronics are susceptible to 'issues' and a good diagnostic device akin to the BBS Nanocom Evolution or Faultmate are a must to keep these vehicles in check.
The diesels mated to an auto box do seem sluggish until the Turbo comes on song, but the accelerator pedal does have a loooooong travel to it so give it a poke and she'll lift her skirt and scamper away willingly.
If it is sluggish to accelerate or on hills, check the pipe to the MAP sensor as these seem to split and the ECU doesn't get boost/manifold pressure information and defaults to a basic fuel map which is woeful!