Reply by BlasterStumps

You might try a wire brush on the spots then treat with WD-40. If they are etched in, might need to sand more in order to get rid of them. One other option would be to put the whole body of the plane in a soak of Evapo-rust or something similar. That would leave the etched areas although they shouldn’t rust afterwards, especially if you treat with WD 40. If you solve the rusting problem you mentioned, the spots shouldn’t affect the performance of the plane.

-- "I build for function first, looks second. Most times I never get around to looks." - Mike, western Colorado