The solvent used should match whatever material is being removed considering the material it's being removed from. Fortunately fiberglass and epoxy once cured, are pretty much solvent proof so match the solvent with whatever you need to remove.
Some tape adhesive residues will yield to alcohol, some won't. Other residues sometimes will dissolve with mineral spirits. For removing old decals and stickers, I've had good luck with oven cleaner. Most cured caulking, silicone sealant and polysulfide are pretty much solvent proof like cured fiberglass and epoxy. For cleaning up fiberglass, usually strong solvents such as m.e.k. or acetone are used. Rust stains in fiberglass usually will dissolve with oxalic acid based rust remover solutions such as those sold
by Home Depot or the dry oxalic acid in Bar Keeper's Friend plus a little elbow grease.
To remove old caulk from fiberglass, first mechanically and thoroughly remove the old stuff; Scrapping, sanding, hammer and chisel, whatever works. Then a good wet wipe down with acetone, changing rags often. Just don't let the acetone touch painted surfaces or foam or plastic.
By the way, urethane foams dissolve in acetone. This feature can be handy as temporary molds could be made of foam, the silicone or fiberglass parts cast, and then the mold dissolved away with acetone. Kind of a 'lost wax' molding method with chemistry.