Re: removing pinstriping
Start with the least obnoxious solvent you can find. Water is the universal solvent, and after you add some mild soap to the mixture remove as much of the gunk as possible. Stay away from strong detergents that can dull the finish. Look for car soaps that are safe for Vettes; however, I'm guessing the gel coat on cars is probably not chemically identical to that of watercraft.
Then move up the scale with some tar remover that contains a petroleum distillate. Call your nearby Chevy dealership to see what is safe to remove road tar from the gel coat on Corvettes.
If that doesn't do anything, then go for Goo Gone Citrus cleaner, but I would go sparingly instead of slathering it on. Work a small area and avoid allowing the solution to go where no sticky material is not. I have used Goo Gone Citrus on the soft bummper covers of my cars to remove the road tar that just won't come off with petroleum distillates for years with no ill effects.
I would NEVER yield to the tempation of using the one thing that probably would remove the gunk in a flash -- laquer thinner! It would eat into the gel coat instantly. It maybe look clean, but in a few weeks or months there would be a dullness of the gel coat that could not be cheaply repaired.
Daniel