Functionally, there is no problem, all significant cast parts on your buggy will be the same - esthetically a real negative! Bob’s suggestion is a good one (never seize) or spot paint.
I don’t drive often, enough. So do see surface rust on the brake rotors. Concerned? No not really. Next time driven, it be gone. And then till next time driven.
I had airplanes with disc brakes, and the rotors rusted. But later I switched to chromed treated disc. Now they not shiny chrome, but grayish color. With no rusting.