[paulk]

Grinding, filling, painting... sounds like a lot of work for something that doesn't sound overly structural on an older boat. Why not simply cut out some black plastic (something that won't disintegrate in the sun!!!) the right shape and glue it (epoxy would be fine if it didn't attack the plastic) over the old stuff? Makes it look even more like a window, and shouldn't take more than two hours, including buying the plastic.