My 20 yr old double dome plexiglass skylight has no visible cracks nor does it leak during a rain. It does let in a lot of hot air in summer and cold air in winter and I can see that the seals in some places have moved. There is some dirt around the edges of the domes.

I started to replace it with a Velux skylight but after removing it, found that the sheetrock extended about 1 inch above the curb and some of the flashing was folded over the top of the curb. There was no sealant or gasket between the frame and the curb.

My questions are: Couldn't I replace the dome seals, add a curb seal and clean the domes? Also, should the flashing that folds over the curb be trimmed off before adding a sealing gasket?