I bought this 9c brand new, traded it to a friend and a few months later it came into play on another trade and came back to me. I was at the range with it a few weeks ago and noticed the rear sight was loose in up and down movement. Question is, is there supposed to be a spring in the sight? I have no spring but it does look like it's possible that one goes there so if someone could take a look at theirs and see, I'd appreciate it. Thanks.