I've had very good luck with Self-Etching primer, then a top coat or two of spray enamel. Lacquer works, too.
I use it in the bed of my tuck where it sees lots of abrasion. The self-etching grips both the metal and the paint.
Maybe spraying on a clear coat of lacquer or epoxy will give your part a more durable finish, but it'll eventually have the problems that Steve123 mentioned. (Door knobs, lamps, hinges & other brass household sutff have a clear coat over the plating.)
A paint chemist once told me that Rustoleum has fish oil in it, so it never dries completely. It feels dry, but isn't. That is why it's not terribly durable. You can scratch it with a fingernail. The never-drying additive is the magic behind why things painted with Rustoleum (and Krylon Rust Tough) don't rust. The paint expands & contracts well and never gets micro-cracks for moisture and oxygen to reach the metal. Cool, huh?