I use Megs #4 heavy cut cleaner and a wool pad ( white) to rip the oxidization be it light or heavy. If it's really bad then I wetsand with 1000 grit and then polish it back with #4.
Gelcoat does not have a UV inhibitor in it that is why it fades so fast. I hear stories from boat owners all the time, they polish the boat and within 4-6 months it's faded again.
I use a unique product called X-Kote.
X-Kote Paint Renewal Systems Inc I apply this product overtop of my polishing work. X-Kote bonds to the gelocoat permanently giving the boat a layer of actual clearcoat. It enhances the color underneath and gives the surface a layer of UV protection that is far superior to any wax or sealant on the market. Why? because it never washes off like wax or sealant. I have boats going on 2 years now that still looking wet, glossy. All the owners have to do is wax the boat once or twice a year like you would wax your car. Takes 40 minutes and no major expense to have it polished.