Fiberglass repair

What you use to take it off depends a lot on what the mark actually IS. Kind of hard to think of what might fall and LEAVE a black mark. Is it high on the cap? Down where a bumper or something like that may have hit it?

Probably won't hurt to make a few guesses other than purchasing things without knowing what it's trying to remove. Knowing would be better.

Goof Off. Rub lightly.

Try Mr. Clean pads. or,,,, a polishing compound.