You sure you don't have real rust on plated steel grates? To best of my knowledge GBS grate ie nickle plated steel. I would steel wool or sand smooth if they are. If grates get too pitted they hold too much grease and don't wipe clean. Brush food off after cook and oil. Wipe clean before cook. Buff off any rust that gets started, usually over fire area where seasoning gets burned off. They will eventually season up nice. Sometimes I think plain steel would be better because they season well after they rust a little and the nickle comes off some. I would treat Stainless same way.