I doubt it's the valve stem seals since it smokes all the time, not just when cold. If you have low compression on one hole pressurize it with compressed air and listen to the intake, exhaust and crankcase vents to see if you can hear where it is leaking from. Can't really tell if a valve is burnt or carboned up without pulling the head, but if it has been sticking open for awhile it is probably burnt. Perhaps your turbo seals are leaking?

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine