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You say you have oil running out the end of the exhaust? Sounds like the turbo seals have failed or not properly installed. The seals are like small piston rings, and must be installed with care. My 1982 300D-Turbo was doing the same as your car.I called M&D Distributors in Houston,TX and told them what my turbo was doing. Blowing oil out the exhaust pipe. The salesman called me back and told me what I needed. The cost for parts including shipping was $22.31. There is not much to a turbo. It was fairly simple to rebuild.
You say your car starts good and runs good, so I don't think rings would be the problem.I would have the turbo checked again. It could be defective. I have gotten new(Bosch rebuilt) starters and not know they were bad until they had been installed. Of course the dealer will replace it, but you have to take the bad one off and replace it.
Good luck..
Bill Lewallen: Lexington,Ky. Where diesels purr and turbos whirr