Rust has a way of creeping up on you, doesn't it? I was looking over my car today and discovered that three doors have rust in the rear corners, right near the drain hole. So far it looks like only the outside is affected, but the rust looks like it's underneath the paint. Does this mean that it's actually rusted from inside out, or is there still the possibility that I've got surface rust? I don't want to start grinding away at it, only to see a big gaping hole in my door. I've read some threads where some people have resorted to looking for new doors, but I'm really hoping to at least stop the rust from getting worse first.