I need your help, my 1981 300 D shows the inferior surface of air cleaner case stained by oil, oil drops over the manifold intake area. Tha air filter is partialy plugged by oil. Thank you.

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Juan

You probably have a tear in your vacuum pump diaphram... pretty easy to replace....

I have the same thing and the blowby from the valve cover breather hose is what is staining my air fliter. Have you checked the blowby by pulling either the breather hose or oil filler while the car is running?
How long has it been since the air filter was replaced?

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Thank you to Leathermang and Fisherman
for your help. The car never has run without air filter. Looking for the cause of the malfunction of the PVC system I have installed a rubber tube from the vent insert to a plastic bottle I have made a lot of holes that way I am able to observe the blowing (a lot). I have placed another tube from the draining tube situated in the inferior surface of the air case to another clear bottle, to cheek the draining. In both bottles I got oil.
I would like to know if the problem I have is malfunction of the oil separator or the differential pressure valve located in this device or in the vacuum valve.
The car run nice.
Juan

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Juan

So you are sure it is not a hose connecting the vacuum pump to the middle of the air cleaner which is putting the oil into the filter ?
If you are sure it is the PVC system I have no experience with that system.. I have been lucky...