Rust in pitted metal... It's a pain, it WILL come back to bite you, and it can be frustrating to remove. Our first choice will always be to media blast, but that's not always possible and it can be a mess. You can use fast etch or another phosphoric acid and that will quickly dissolve iron oxide completely. Lastly, if you don't have access to the first two, then you can use rust encapsulator to fill in the pits. Cody used this method on the Camaro project and it worked like a dream. Encapsulator