Both products are safe to use as directed on gelcoat and painted marine surfaces. Apply FSR with a brush or towel, or just spray on the Star brite. Rinse thoroughly after it sits for a few minutes. Repeat on stubborn stains. To prevent stains from recurring, replace the offending piece of stainless-steel hardware and be sure to fully bed the new installation with a marine sealant, such as 3M 4200, to minimize crevices.