I have seen a lot of 240d cars from the 123 series with oil all over the top of the engine. I once asked a mechanic about this and he said it was from a worn timing chain. It somehow got everything a little out of whack and created a lot of pressure in the crankcase which resulted in the oil blowing out of somewhere. And that somewhere was usually the oil flller cap.

The car seemed to run fine.

I think these oil catch cans spoken of earlier were common on the 111 and 110 with power brakes. Since they took their vacuum right off the crankcase part of the engine it was just a matter of time before they started sucking oil in a vapor form into the brake booster. There the oil would cause the diaphragm in the booster to break down. But with the inline catch can you could see oil collecting in the translucent can before it caused any damage to the booster.

Search Ebay or a wrecking yard for one of these inline brake booster oil traps. I don't think they are that expensive and with one inline between your crankcase hose and the air filter you would be able to see if this is where your excess oil is coming from.