I had such a problem many years ago in my 76 Volvo with the renault v6. I cleaned the crankcase ventilation system and it cleared up. I don't know what you have on your system but perhaps it is pcv related.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.