I just use industrial enamel, its about $50 for a 4 litre tin, works for me. No matter how hard it is, it will rub off the parts of the attachment that are in the dirt.
Deal with the rust first. Eastwood makes some great products in that area. Then a good enamel. But as Tazza mentioned, the area of the attachment that touches the dirt will have the paint removed no matter how good or expensive it is.