So I finally got my hands on a Gen 1 P99 (been wanting one for a while), and the rear sight was installed improperly (literally flew off when sending the slide forward). I have two pieces--the sight itself (with screw/bolt), and the plunger pin. Problem is, when I put the plunger in the hole it goes in it just sits flush and doesn't, well, plunge. I have to punch it back out through the other side. Am I missing something or some kind of part?