i just replaced the oil pan gasket because it was a little leaky and, looking from beneath, noticed some scratches in the metal up above the oil pan. i didn't see any metal in the bottom of the pan and everything looked fine as far as i can tell, but i'm not sure i'd know what to look for. engine runs fine, low compression (160) in 4th and 5th cylinders. is this normal or should i be worried?

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1980 300D, 128K

Probably done when it was built. Many parts have "scratches" from coarse machining to remove casting edges.

Low compression in adjacent cylinders (4&5 in your case) is a sign of a possible head gasket failure. There are other possible causes as well, but a head gasket leak would be a (relatively) good thing. A (relatively) inexpensive and (rel...) easy fix. With such low mileage, I wouldn't expect worn rings or burnt valves, but stuck rings are a distinct possibility. Rings tend to stick more from lack of use and short trips.

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1987 W201 190D