Metal-to-metal fillers are also useful on old cars that have a lot of rot. The metal filler has incredible bonding properties and can be an alternative to totally replacing a panel. Of course, the correct way to repair a badly rusted area is to replace the metal, but it all comes down to how much time and money you have. In our case, we opted to use filler called All-Metal to repair a rust-corroded area of our Nova’s roof, after using some DuPont rust treatment to chemically seal the each area. We’ve been warned, however, that simply filling the holes will look fine for a while, but it’s almost guaranteed that you will find rust bubbles under the paint in time.