Rust inhibitors/converters work well but need to be followed up with some kind of coating or they will eventually rust again. I used KBR products on my frame and diffs and it seems to work pretty well. They also sell in various colors which other similar type products dont. They sell a combo trial pack which is what I used for my diffs. Its fairly easy to use and inexspensive but it will stain whatever it gets on so if you use it make sure you mask the area very well including your exsposed body parts ie hands, face, hair etc.