I have a 1997 300 TDI automatic Disco which I bought two years ago with 120,000 miles on the clock. Now on 150,000 miles and it's needed a set of glowplugs and a new diesel lift pump. Both less than fifty quid and half an hour's work each. Two services done by a local independent, and he found no problems either time.
Oh, and I'll probably have to replace the battery in the next few months.
Other than that it's reliable, comfortable, and surprisingly economical. Getting about 32 mpg average which is not bad for such a big, heavy car.
I too have a 1993 200 TDI Disco, and I love it. Economical, comfy and good off road. They're old cars now, but maintenance is easy and really pays off.
Most will need new Panhard rod bushes, a new A-frame ball joint, and new shocks and damper - these will make it drive like new again (almost).
They're not for mechanically inept people as they really are an off-road performance vehicle in sheep's clothing, and should be treated as such.
They are superior in most aspects to the Land Cruisers and Patrols of the era, and have far more character.
I have a '93 Disco TDI, bought new those many years ago. Still working like a dream and very few problems. Now about 110k miles on the clock and just modded to be better off-road (lift, tyres, protection, etc). Otherwise all mechanical parts are the same - not bad for a car that has been skiing, diving, sailing, around europe, towed boats every weekend, swimming in the sea, etc. A terrific car that has NEVER let me down, with the exception of some minor clutch niggles.