Just got a chance to use a product called "Spotless Stainless", introduced on Sailnet a few months ago, and am pleased to report that the stuff is every bit as good as the chap said it was. This is a product that is a creamy white gel one applies with a short bristle "acid brush" to the affected rust stain. Leave it on for 30 min and hose it off. I find I'm more comfortable using it than I am with FSR, also a gelled rust stain remover. I haven't used Spotless in general stain removal applications on gelcoat as I have with FSR, but as far as Stainless cleaning is concerned this stuff gets my whole hearted approval.