I put a pair of Power Stop Evolution Premium Coated Brake Drums on my car. They looked good. But after about two years they started getting rust spots. After about 5 years, they look pretty rusty, almost like any other drum. Might as well as save some money. Next time I get uncoated drums, the cheapest I can find. It doesn’t effect performance or functionality. I suppose you could try caliper paint. Or maybe get evolution coated, then put POR-15 on top of it, then caliper paint on top of that. Never tried it. Would be kind of worried that POR-15 would effect rotation because of the extra weight. I have basic stainless steel rims, can’t see the drums anyway unless you take the tires off, so waste of money. When in the rust belt, there’s not much you can do to stop rust. I’ve heard that powder coating is even better than spray paint, as far as preventing rust.
Like others have said, might as well as worry about more important things that effect functionality.
I don’t know if the calipers on my Corolla are rusted or not, traditional steel wheels w/wheel cover, can’t really see caliper, so haven’t noticed. I expect OP likes the Porsche look, no wheel cover, wagon train wheels with thick sparse spokes, allows you to see the painted caliper. If OP doesn’t want a solid color paint, just have to searching to see if there’s a clear coat that’s compatible with high temperatures. If there is such a product, remove existing caliper, remove all the rust, apply clear coat, reinstall. I expect better results by just using caliper rated paint.
One note, if caliper is highly visible, it is just as highly susceptible to road grit contamination.
This post caused me to look at my calipers. Nine year old truck that is exposed to salt air, yes calipers have surface rust. At least half the caliper is obscured from view by the wheel. My car, a 2020, has larger wheel openings, calipers are more noticeable, not yet showing rust.
IMHO, the only practical solution for calipers are covers, though caliper paint is available.
In Minnesota and South Dakota, I have never had to replace a rotor or caliper or drum due to rust. Warpage and gouges, yeah but not rust.
I’ve used POR15 and like it, but in my experience it does not stop or arrest rust. It forms a nice hard ceramic like coating while the rust continues underneath. On brake parts, I would be afraid of pieces chipping off. So Just use a heat resistant paint designed for that purpose and be happy. Personally I think painting those parts detracts from the wheels. Do you want to see the fancy wheels or the brake parts behind?