<font face='Comic Sans MS'>I've used a Rust-Oleum rattle can red oxide primer for rusty metal that seems an acceptable color. One thing for certain; the stuff is as tuff as nails. The only downside is it does take a day or better to cure to the point where the part can be handles if that necessary.</font id='Comic Sans MS'>
Try some DP74 it will give you the somewhat shinny look of the original paint (rather than the flat open finish of other products. You can tone or tint is a bit if you want to get closer to the original color (I do)