My 300CD has no oil loss over an oil change interval. It doesnt have enough blowby to move the cap at all when running, but the oil mist doesnt very effectively separate in the valve cover. What happens as a result is that it eventually collects (in my case) in the turbo U-tube and leaks out onto the wastegate because the seals get very hard and therefore don't seal well.
Tools:
Ratchet with 10mm socket
Flat blade screwdriver
Black oil-proof RTV
What you get is this:
Others will sometimes get oil in the air filter element itself, I suppose if the blowby is too bad or the leaking from the separator is too leaky.
Some common things that one sees are:
What I see is that the separator isnt separating properly. Instead a lot of mist comes into the U-tube.
Now, why am I sealing the separator? Because mine was loose, and I thought that perhaps there was enough "slippage" of air that there wasnt enough centripetal force to get the oil separated on the walls of the unit. What's the worst that could happen???
The first thing to do is remove the air filter assembly and then remove the right-angle vent tube from the separator assembly.
Then, take the flat blade screwdriver and pry up the two bent metal tabs that hold the cover down.
Then remove the cover.
The product to use is RTV black, the oil-resistant variety.
Apply this to the cover and to the lip on the separator body.
Press the cover down hard and then bend the tabs back to keep the cover tightly in place. Remove any waste excess RTV from the assembly that may have been squeezed out when putting it back together.
I would recommend replacing the two oil seal rings on the U-tube. THey should be part numbers:
Intake Pipe Seal OES GENUINE W0133-1635476
Turbo Seal Ring air Cleaner Hose To Turbo. OES GENUINE W0133-1634936
They can be VERY hard and require a good deal of force to crack them and break them enough to get them out of the U-tube.
Re-assemble as you would put the air cleaner back together. The U-tube is attached to the air cleaner and then that is connected to the turbo.
Done!