on close inspection of the "leading edge" skin holes, i found some ugly drill marks.
i suspected this might be the case. reason being is that when i was match drilling the ribs, the rib noses weren't flush to the skin and as the drill bit went through the skin and found the rib, the bit tended to "walk around" or "chatter" from the rib and skin being slightly misaligned.
i thought about drilling out to the next bigger size rivet, but once deburred, the hole doesn't look nearly as bad.
