Rusted Flashing. Steel metal flashings exposed to the elements can rust over time. Today’s flashings are made of galvanized metal, a process that protects the steel core from rusting. I have found rusted flashings on this roof. Rust cannot be simply sealed over, as it will continue to grow. The rust needs to be cut out and a new flashing installed, then sealed properly. Since the rust is open to the surface and flashings are vital to the integrity of your roof system, we suggest repairing the rusted flashing areas before seepage causes structural damage.