like any other car really just try and get one with full service history pref dealer or jag specialist, do a car check, think one of the main probs on 3.0d is DPF but if use something like BP ultimate fuel or every 3rd fill up and give it a good run now and then should be fine, i,m sure someone else on here has some more tips for you oh and would check any advisories have been done on MOT