Brush-on POR-15 (POR = Paint Over Rust). Just did two coats on my frame a few weeks ago, too early to tell longevity but it looks great and goes on thick. Miserable work though, be sure to wear gloves and sleeves or you'll have it on you for weeks. I've used the Rustoleum spray a number of times and it doesn't last.I was thinking about cleaning up my rear axle and coating it with something. I know I will not be able to get it all down to metal. Any suggestions as to what to use to coat? Rustolem or some kind of undercoat spray? Thanks for comments