ours has the spacers as well. If you have a Lowes nearby in the specialty hardware drawers you can find some stainless steel screws that are 2.5 or 3" long that have different powder coated heads, though any long screws will do. Stainless is best. Our wings are red so the powder coated red heads work for us. I would also suggest that you put some butyl putty over the hole before running the screw in, seals the hole to the spacer and keeps unwanted water (if any tried) from getting in.
If you can't fix it with a hammer you have an electrical problem.
Be careful with the length of screw, keep in mind that your interior walls are only 3/4" thick until you int the 1/8 interior plywood.
Most wings were held on with Pan Head Sheet metal screws. Not sure if they were #6... as most of the screws on the camper were. They may have been a bit larger. ITs totally worth using stainless if you have Aluminum wings.
IT depends or your year if you need the spacers (about 1/2 inch long), I think 1961 (maybe 60 and later) will need spacers. Prior to that the molding is cut as harrison described.
I have heard some early years didnt have anything behind the aluminum skin for the screw to bite into (no wood). Pretty crappy of you ask me but that is how they were.