Went in there to change one to afci and found this. Is this corrosion? And why is it only one? I know most of the house breakers are on the right, but it never feels warm or hums. I really hope this isn't going to be a another problem to have to get fixed. :( Here's a large pic of the entire...

I just bought a used motorhome (1985 Ford Elderado) which has a lot of oxidation build up on the exterior - does anyone know how to remove it? or a compound that will remove it? I believe the exterior is fiberglass. I don't know if just a buffer would work or if I need something as an abrasive?