Seems like positive crankcase ventilation to me. It should probably be connected to the air cleaner to be sucking all that stuff back into the intake instead of spraying it all over the motor. I don’t know.

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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,