Not sure this is applicable to your situation but when powder coating old components such as calipers, wheels or intakes it is advisable to pre-bake the items, prior to coating, to force contaminants out of the metal pores.
I would think a good solvent cleaning, followed by a baking at 350° or so and then finished off with another cleaning prior to painting would give you a good chance of success.
My 2¢
Larry