Evapo-Rust will desolve the rust down to bright metal! A light coat, applied periodically after the initial derusting, will preserve the metal. It is non toxic, fume free and won't harm paint or plastic. Sold at auto parts stores like Advance Auto. The rusty part must be completely submerged or covered with the liquid for 20 minutes or so. Deep pits may take more than one application. On bicycle tubes I have used small pieces of the blue paper shop towels completely saturated then wrapped in plastic kitchen wrap. Smaller parts can be submerged in a small container. I keep some in a coverd plastic bowl for this. Can be used repeatedly. The rust eventually settles to the bottom as a fine sludge.