and what is THIS?
 

I've found something "new" with the '72 220D's motor, new to me. Underneath the air intake hose that goes from the oil bath up to the top of the engine (compartment)... is what looks like a rubber fitting for a hose to fit into. It's attached firmly and appears important. I checked it with engine running and a significant amount of air was moving through it. Would someone knowledgable enlighten me please.

My guess is that it takes a hose from the valve cover. Compression that gets past the piston rings (blow-by, some is acceptable) is routed to the air cleaner to be ingested by the engine so you don't leave a [second] trail of oily smoke.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD