No specific product for black streaks... sorry. At least not yet. We've thought about adding a black streak remover to the line but just to note, any liquid strong enough to remove black discoloration out of a porous gel-coat surface is going to remove the wax or sealant.
Our
Marine 31 Gel Coat Spray Wax Plus has some light chemical cleaners in it and if used shortly after the black streaks appear it "may" be strong enough to remove the streaks and leave some gloss and protection behind.
Another option is to apply our light cleaning cleaner/wax the
Marine 31 All-in-One Gel Coat Polish & Wax by hand or machine.
The chemical cleaners and diminishing abrasives in this product will remove the black streaks and leave the surface protected at the same time.