i always look to the simple things first. have you changed the oil? if not so that and use a good diesel rated oil such as rotella. it does sound as if a seal could be going out in the turbo (not a simple thing). the oil past the valves thing would not come on fast but very gradually over time. the ac and tranny both can easily be vacuum leaks. (a simple thing). good luck.

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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.