I've replaced the drain tube seal and there definitely is no check valve. It is a possibility that I installed it wrong and the tube is below the oil level. Another possibility is that my home made ccv system is causing too much restriction and not venting properly.

Now there's a crucial nugget of information that might explain a lot. Got pictures?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

excuse me,on my SD someone had took the inside of rocker cover apart and resealed it.I've never none what they serviced.Maybe this area gets clogged and blocks flow from breather tube.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

So I just put the turbo on and disconnected the ccv and guess what? No smoke. I would have thought my turbo seals would be toast but they are somehow sealing now. The only thing I can figure is that the excess crankcase pressure blew oil through the seals but didnt blow them out.