on my rear passanger door there is a little crack and I can see some rust, does anyone know how to fix this before it gets really bad?

 

I believe that if you provided a picture of this...it would help...

 

Once it starts, it is near impossible to fix. If you do fix it, chances are that is has started somewhere else also. Rust is really terrible.

 

got to the hardwere store and ask for Navel Jelly, Its a rust removing stuff, kinda pink in color. it also stops rust. OR you could find some of that paint that sais taht you can paint directly over rust. Both of these have rust inhibitors taht will stop the rust. you will have to paint after you use the navel jelly thou.