Are they rust stains from the ferrous magnets? If so, can the paint be more safely isolated by placing a plastic sandwich bag, or other small, thin piece of plastic wrap, between the cover and paint?
If it were to be rust, a dab of vinegar water might safely remove the stain.
2019 Leprechaun 311FS
Wes, Linda & Quincy (std. Brown Poodle)