I used Polyglow on my old 1997 National Seabreeze. Only used it on the lower portion that had blue/green gel coat that had severely oxidized. After you clean it with the prep, the finish is vey dull and flat. The Polyglow is like floor wax...puts a shine on the dull finish. After a year or so, it starts to wear off, so you have to do it all over again.
Doesn't shine like the original finish, but it looks better than before.
I removed and replaced the decals on our Montana. You have the outline (or shadow) of the decal because the gel coat that was covered didn't oxidize because it wasn't exposed to the elements. The gel coat that wasn't covered oxidized and turned yellowish.
There is no product that I know of that will remove the oxidation. I ended up using an orbital electric sander with 220 grit and lightly sanded the gel coat until the oxidation was removed. Then I used 400 grit and then 1000 grit wet sanding to remove the scratches.
Then I used an electric car polisher with wool bonnet to buff the finish, first with a coarse polishing compound, and then a finishing compound to bring the shine back. Then I applied new decals found on EBay. They didn't exactly match the originals, but were close. At least you couldn't see the shadow from the old decals.
It took me about 4 to 5 days to remove the decals, prep the surface, and apply the new decals. Way more work than I thought, but once I started, the job had to get finished. I only prepped the areas where the old decals were, way too much work to get the whole rig shiney again. After 2 years, the prepped areas are starting to oxidize matching the rest of the rig.
'05 F250 6.0 Bullet Proofed
'02 Montana 3280RL Upgraded a bunch.