Another thing to keep an eye out for is affectionately known as "black death" on these Mercedes OM642 engines. (Google it for scary pics!) You won't be able to see it unless you pull the engine cover and foam sound dampers... But you might smell diesel fumes if it's present. All it really is, is a leak between the injector and the cylinder head. It leaks combustion pressure and gasses. This is another reason why It's always good to have an experienced mechanic, and in this case a diesel specialist, do a thorough pre-purchase inspection.
Personally, i don't think it's a deal breaker on an otherwise good find. But it has the potential to be a costly fix, so that should factor in.
A slight disclaimer/story here...
I'm a fleet mechanic, and former European car specialist, so things like rust and body damage scare me, while i tend to dismiss most mechanical things as " Well, i can fix that..." Makes me awful at suggesting what to buy! Lol.
Anyway, I actually found out about this black death thing with my own CRD purchase... After... i drove it 1300 miles home from the dealer... I've had the parts to fix it for about 6000 miles now... So you can see how much this really concerns me...
But it really does need to get fixed. It only gets worse the longer it's left alone.