Have an 84 190e 175,000 miles with a similiar oil leak problem. I have not looked in the air cleaner lately but it is losing oil from the valve cover gasket(I think)
and possibly from the head gasket. I replaced the valve cover and gasket and still have drops of oil under the engine. I believe it is coming from above the exhaust manifold. I have the valve cover torqued at 25lbs currently. The manual call for 17lbs. Tightening the valve cover bolts on the exhaust side first reduced the amount of oil loss and changed the pattern of the drops under the engine. My next step is to go to 30 lbs torque and make sure the gasket is seated properly.
Appears the oil in the air cleaner may originate from the PCV.