Hello to all. Recently I bought an old motorcycle, and it has small rusty spots on frame, near some original welding. What can I do to get rid of this rust without dismantling the whole bike? I have a bottle of phosphoric acid and I was thinking of getting a rag soaked in acid and cover the rusty part with it, and then paint the part with a small paintbrush with oem color. I'm not thinking about getting rid of the rust with something like sandpaper because it might weak the frame, don't you think? And will phosphoric acid corrode the painted part? Thanks.