That's a lot of money for the car, even for an ES!

Is it from a dealer?
My '94 300tdi (with the comfort pack and air con) was immaculate when I bought it 5 months ago, and it cost me £2750. It had 101,000 miles, with 80,00 main dealer serviced.
If I were considering that Disco, it would have to have full dealer service history, and everything would have to be working on it! Even then I would haggle down, if possible.
Makes me feel better though, that my Disco seems to be worth a lot more than I paid for it!
If you're set for it, listen out for for a whistling turbo (it's NOT supposed to do that!), leaking windscreen/leaks around the rear pillar speakers (try and take it out in the rain; some unscrupulous sellers might clean off the wet marks, giving the appearance that all is well), rotten boot floor(lift the carpet up), switch back lights inoperative (bargaining point, but cheap and easy to fix), dodgy alarm/immobiliser (don't touch the car with a barge pole if this doesn't work!) and of course, the usual engine checks. Oil around the head isn't a problem, unless it appears to be too excessive.
Remember that smoking on start up is not a problem, but if it persists, its not good.