How many miles on it?

This engine is known for serious oil burning, following an internal event that slightly bends a rod ... once this happens, it's engine rebuild or replacement time.

Might be something else, but my understanding when it happens you go from normal ops to massive oil burning very, very quickly.

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg