82 300D - What type of damage can occur if the engine was overfilled with oil?

Went to look at purchasing this vechicle and everything about it was great even with 260K miles, but I found out that it it was just recently overfilled with oil and that their mechanic stated that one
of the cylinders will need to be replaced or repair.
Why is this? The only thing that I can remember is that if a typical engine is overfilled and run too hard, it will destroy the oil seals.

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