If you like the car but the engine's shot (and if you ran it out of oil, compression is low and blowby blows the oil fill cap off, it kinda sounds like it), there are enough W115 240D's around to find a replacement engine from a rusty heap with a running engine - and you'd have lots of spare parts to boot.
However, if you decide to part it out, please PM or email me as I still need a passenger side horn and passenger side taillight assembly for my '76.

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1976 240D "Katja"