My 240D had 153000 on the clock when I bought it. The records showed very few problems (an a/c problem was repaired, steering box was adjusted, belts/hoses, motor mounts, flex disks and shocks changed).
I got a good deal on it because it needed injectors, and I think the previous owner thought the pump was failing so he was open to an offer.
My 87 sdl needed all of the above at 165kmiles plus....tranny front seal (ouch...that one left a mark on my wallet), left side half shaft, a/c repaired several times, and lots of front end parts. When I sold her, I think it might have needed value seals (puff of blue smoke on startup).
I admit the 300sdl would eat road like no other car I've owned...the turbo would kick in about 72 mph, and at 80 mph, it just hummed.
Oh, yeah...remember that the 420 is a real gas hog...I believe it will get about 15 to 17 mpg...my sdl got about 24.