There is no oil seperator in the air filter on the four cylinder. The seperator seems clear on this car, and the engine is strong with no blow by.
Your 240D can probably be fixed be making sure that the tube from the top of the valve cover to the manifold is sealed.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in