You might try some oxalic acid on them. Bar Keeper's friend can be mixed into a paste and put on the affected areas, this will neutralize the rust. Probably scrub some with a toothbrush or the like to help it along. Apparently Bar Keeper's friend also comes in a liquid, but I've never tried that. Wrap with some damp paper towels and let sit for awhile. When the rust is removed, I would clean and touch up the areas with something like Testor's enamel model paint to protect it. Let dry thoroughly, heat will help.