At my local gun dealer, I saw a used 870 Classic Trap yesterday which looked to be in good shape, not shot much, but had what looked to be surface rust on the rear of the rib (thick part where it attached to barrel) and some small spots of surface rust on the side of the receiver. Is there any way to remove this without re-blueing the gun. Also, if I were to keep the gun with a light coat of oil, would that keep these small spots from getting worse?