The original engine on my 240D 77 lasted about 300K, mostly stop & go city driving, at the end it was smoking blue pretty bad, the oil used was Castrol 30 weight. I replaced the motor with a new one from the dealer and am using Chevron Delo 15/40, let us see how long this one will last. Oh, I do change the oil/filter somwhere between 2K & 3K miles.
I did not know that there was such a thing as diesel formulated oil, learned about it on internet.
If your engine is in a good shape with no oil consumption, I would go with one of these diesel rated oils.

Thanks
Vahe