Could be a nice car when sorted out.

There is a history of OM602 head issues, however that IIRC was only the early 602s, and I'm not sure that it ever went past the '87 602 turbo. The FSM has the head casting numbers and history. Also, be sure that if you replace an OM602/603 head, you only use a turbo head on a turbo engine (different castings also, consult the FSM).

Your car sounds like it might have some rusted cylinders from water/coolant sitting in them for a period of time. If you plan to keep the car, remove the head and check cylinder condition before you get much further. Also, if the turbo was seized, have it checked by a turbo shop, a seriously bad bearing/seal will let enough oil past the seal to run the car, and it won't shut down until it runs out of oil and destroys every moving part.

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Gone to the dark side

- Jeff