Blowby routing.
On the '83 240D I am rebuilding I put the original configuration back in - that is what I call a "cyclone separator" (don't know the real term) back in. This system separates the oil fumes from the liquid and returns the liquid back to the oil pan. The fumes go into the intake downstream of the filter. I had the option of going with the '80 manifold arrangement which does not run the separator and justs dumps the blowby back into the intake downstream of the air cleaner. I figured I may as well recover as much liquid oil as I can. The '85 300D has the separator in built into the center of the air filter so the vapors go into the air stream after the filter.
I will see how it goes with the 240D, it should be ok because I replaced the "o-rings" on the return line and installed new hoses around the separator but if it makes a mess externally I will go with the 1980 arrangement.

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Jim