I have had several Mercedes Turbo Diesels and several trucks with turbo.. All high mileage.. When a turbo seal goes out it can leak both ways.. Into the intake and into the exhause.. Laying down a lot of white or light blue smoke.. Its kind of hard to get any engine to smoke that much with out breaking a piston or some thing like that.. If it runs fair and on all cyl.. Odds are its a turbo Seal.. This is just experance talking..

Snowdance