Early diesels are relatively rare. So can hold a higher price than the petrol versions. The motor is not great, but will slog away forever.
Look for rot in the boot under the lockable cover.
At 83k, you shouldn't see any major problems apart from routine wear and tear. Check the VC works properly. If you get excessive 'scrabbling' on full lock, it may be faulty. All of them seem to do it a bit, but if it feels like it really doesn't want to go round, it could be a problem.
Not aware of any issues with the gearbox, but others may be able to advise on this.
Some of the switchgear seems to be a problem on earlier models. Check everything works.
Rear door glass mechanisms can fail. Check the glass goes up and down OK (should drop about 1" when you open the door).