My '92 300E had the head gasket replaced at about 75K. I bought the car with a little over 100K. At some point I started to notice the need to add oil mainly after long interstate runs of 400 - 600 miles. Also noticed very slow loss of coolant.

I was able to eyeball the leak. Passenger side 2/3 r'd of the way back toward rear of engine. What happens is that the oil gets caught in the airflow and creates an oily mess on the bellhousing. Mine looks a lot like yours.

I have now been adding oil and coolant for around 130,000 miles. Engine runs fine with no cross contamination between oil and coolant. Plugs are normal.

This is not to say that is your problem. Could be valve cover gasket leak. Jack it up and crawl under there with a flash light. With engine running you should be able to see the source of the leak on the parting line between head and block.

Steve