I'd stay away from the '89 300E with 317,000 miles. Ask why the mechanic who did head and valve work on the BMW 635csi is selling it. Not too many folks put a lot of time and effort working on a car and then turn around and sell it for next to nothing. You need details on the car. What else if anything does the car still need repaired? It could be a money pit.

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Fred Hoelzle