Mine eventually came up in big flakes, and as I sanded to get to a place with good primer/metal adhesion I wound up doing a 6"x9" area. Of course I didn't take my time doing the paint and the color in the rattle can from Wal-Mart didn't match so it looks like ass, but from 10 feet away it's not too bad, and it looks better than a big rusty spot on the hood. Repaint is the only way to go.
Scott
