Acetone has been used to clean gelcoat for decades. It will not hurt the gelcoat unless allowed to set for a long time, such as a rag that is soaked in it left laying on the gelcoat. It will strip off any wax, etc. Probably a lesser solvent should be tried first, but if all else fails the acetone might work. I say might, because once the Cetol has dried it will be difficult to get off. We use exclusively Cetol on our exterior teak. I have had to carefully remove some that was spilled with a razor blade. It is always best to clean it up before it dries. ChuckAcetone ... but beware, it is not nice to your gelcoat.