I have a series 80 mark 4 colt 1911. It has been a great gun but I just got back from the range and as I was cleaning it I noticed that the rear sight was lose. Not sloppy but I could click it back and forth about a 64th or less before it locked up then I could click it back. I don't even know if it moved enough make a difference at 25 yds. I am worried it will get looser over time. There is not hex set screw or peen mark to lock it up. How do you go about tightening up a rear dove tail sight?