Except for the cracked original head on the car, my 300SDL has had zero problems throughout it's lifetime. I have known 300SDL's with over 400K miles on them. Going strong too, I might add.
As far as overall ruggedness, and durability the OM617, 616 engines are unbeatable, though. But the six cylinder isn't far behind.
I never have to do valve adjustments on a OM603 motor!
I do agree that the new diesels seem to be too complicated. Electronic fuel injection common rail technology and other innovations are nice. Except, the reason I have a diesel is never to be stuck on the side of the road somewhere.
If the charge in the new cars is low(Altenator), then the CDI diesel WILL IN FACT LEAVE YOU STRANDED ON THE SIDE OF THE ROAD. A gasser will do the same thing! I don't know much else about the CDI's, but I know I'd much rather have a nicely kept 4-sp 240D then a brand-new S400 CDI.:p
If the CDI engine only lasts 20K miles, that would be fine. That would mean I would have a car for life, with 4yr or 50K miles warranty on each motor!
What was said about the E290 turbodiesel is true. They didn't last long until Mercedes started having problems with them.