Well I have been working a problem for the last couple of weeks, not very seriously but working it.
There appears to be around the turbo oil return line and air filter oil seperator return line at the upper oil pan in the 300TD, a oil leak.
Also in the air filter is a accumulation of oil. The oil is on the inside, filtered air side, of the air filter, not on the outside, fresh air side, of the filter. So its probably coming from the oil seperator that the PCV system uses.
The blowby when disconnecting the vavle cover to air filter line is not excessive.

I have done the following.

Replaced turbo oil return tube gaskets at the turbo, tube seperation point and upper oil pan.
Replaced the Orings to the air filter oil seperator, upper and lower.
Replaced the valve cover to airfilter tube with the new designed unit, which I have been told, helps prevent a lot of oil from going into the air filter seperator.
Made sure the oil seperator in the air filter is clean, sealed and working correctly.
I vacuum tested the air filter oil seperator drain line, check valve. In the upper oil pan is a check vavle that is supposed to prevent oil from being sucked up into the air filter. THIS TEST FAILED. I tested it by using a Mityvac. Used some ribbon chaulk around the large drain tube opening to seal the rubber hose of the Mityvac. I could not hold a vacuum. IS THIS TEST METHOD CORRECT? Or does anyone know. This definatelly could be the problem. The Tech at the dealer, who is reliable, has never had to replace one of these.
Replacing the check valve requires removing the oil pan.

I will also adjust the valve and install a new valve cover gasket. A little seeping at the valve cover, but not alot.

My main question is on the oil seperator check valve test. Has anyone done this and what are the proper test proceedures.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car