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Sounds to me like you need to open it up and repair the wet area(s) of plywood. Could be an easy job with a grinder, some filler and re gelcoat. But it could be opening Pandora's box. Rarely have I come across a wet screw hole that was limited to a small area. If it's not delaminating or showing big stress cracks and the boat otherwise has no signs of being waterlogged, it's probably not a huge concern.