I have an 82 240D and it has a separator outside the air filter (mounted on the front of the intake manifold, in front of the air cleaner). It's hooked to a vent off the top of the valve cover and has an oil return line at the bottom that runs down to the engine oil sump. The separated air goes into the air filter housing. I don't have a picture or a part number, but I can look to see if there is a number on it. I have looked for replacements in the past, as I wonder if this thing still functions. It has been a leak source at every connection. I have never seen a replacement that is sold. I took it off once, but could not get it apart to look inside...probably just works like a cyclone separator???

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold