If it is indeed blowby from wear, it's the rings that are tired and pressurizing the crankcase, not the oil possibly getting pulled in past the valve stem seals. Or it could just need a new oil cap gasket.

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1985 300D-189k The 'UD', Ivory and Pinkamino
1979 300D-211k Dark Gray, Parchment
A 1980 Harley-~166k and
A 1994 Ford diesel pickup-349k and
A 1990 gasser Volvo wagon-145k