I have a 200tdi, no problem getting parts in general, and cheap. Reliable, simple, good motors. Cylinder head you can't get new so run a good temp gauge and low coolant alarm. Don't boil it and you won't need a new CH.

If you crack a head you can get a recon or convert to a 300tdi head. And not much needs to be done to drop in a 300tdi motor as replacement.

If its a tidy disco with a 200tdi, set up as you want, for the right price... its a good find. On discos the 200tdi motor often outlasts the bodywork!