I don't have Brembo brake calipers but I just finished putting on a set of Power Stops on my 300C by Rockauto. Essentially the same deal, I believe which is powder coated brake calipers. I just spray them with Meguiar's Hot Rims wheel cleaner and leave on for 5 minutes and then hose off. They turn out spotless although rust will start forming on your rotors because of the cleaning action. First application of your brakes will scuff off that rust and your calipers will be gleaming.