Get your brush marks out with some medium grade wet and dry (P240), then go over the whole lot to lightly key it with some finer grade (P400-600) then spray over with Hammerite (or similar - Plasticote is good) as Feck suggests. If you go back to bare alloy it gets complex because you'll need to use an acid etch primer to get anything to stick, then prime, rub down and finish.

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