[~Whitey~]

well you are in Salt Lake City, things are going to rust there much faster than say here in Missouri. I went to Florida for vacation last year and had my tools in the back of my vehicle stored away in the case that I needed them.. When I got home and put them away they were covered with a layer of rust just like on your mirror nut, not quite that bad, but bad enough. The salt in the air is not the friend of your truck! If it happens again, you may try clear coating them to ward of the rust.