[altcognito]

Rust qualifies somewhat under #2, but not completely. Rust isn't 100% preventable in some areas. I live in Michigan and because we use salt on our roads, if you're not washing the vehicle (along with the undercarriage in particular), you will inevitably get rust. On my last vehicle the engine mounts (which were part of the frame -- unibody) rusted. There was pretty much no way to fix the car soundly. If I had washed the underbody frequently enough I could have saved it, but there is a cost associated with that as well.