they are an interesting breed. infinitly tough but if it breaks it will probably cost you more than the vehicles worth for anything substantial. i think a starter motor is £600 from nissan.
there just isnt enough of them about thats the problem.
the 4.2d is fabulous to drive as long as your not in a hurry. you never need to rev it, great for towing.
and check for rot, any rot near the back end is a nightmare, sills are easy enough to weld up but the back end has a hibit of disintegrating on them. look for power steering leaks etc as they could prove very costly.
bloke down my road has one but its a 2.8 Turbo and to have the head gasket and cam belt done was over a grand. although im not sure if the 4.2 has a belt. might be gear driven.
check gearbox for wear,
basically any faults that havent been fixed previously are probably the expensive ones to fix.