I applied RPM to my rear leaf springs, shackles, drive shaft, and most of the bare metal pieces on the front suspension. I've driven the car almost 2,000 miles since the restoration was completed last fall, and so far, I have not seen any rust on those items that were treated. Then again, I don't drive the car when the roads are wet, and don't live in an area with high humidity or salty ocean air, so that may have something to do with the lack of corrosion as well...