A different approach is to clean the gel coat with Comet, using a
stiff-bristled brush, rinse, dry and then apply Penetrol, a paint-flow
additive. The results are amazing. If you want to spend a little more, buy
Marine Penetrol, but I couldn't detect any difference in the results. The
shine will fade, eventually, and a yearly recoating may be needed. I have
found this to be a really low-cost, rapid method for treating badly oxidized
gel coats. Google returns pages of information on the product and its uses.