What is the condition of the rubber hoses going from the valve cover to the air filter housing? If they are hard and brittle, replacing all of them should solve your problem. When I bought my car, the hose that connects to the top of the air cleaner housing was cracked and blow by gases were making a mess in the engine compartment. I replaced the hose ($6.00) and the problem stopped. Hope this helps.
'82 300D Turbo 222k miles