Ruptured vacuum diaghram?
I don't know details of your engine, but I used to have a 1975 280C, and when I first acquired it, it smoked a great deal, and the #1 spark plug was coated in oil. It turned out that the vacuum booster pump diaghram had a hole in it, and was pumping oil from the engine into the intake manifold, which routed all the oil to the #1 cylinder. You might check to see if your engine also has a vacuum booster pump - my problem was immediately visible by pulling the vacuum hose and noting the oil inside. The car smoked most just after going down a hill. which put more oil towards the front of the engine, I guess. I just removed the booster pump and installed a plate instead, as the pump isn't really necessary.
'82 300D/4.3 V6