It's not just the LC9. I almost lost the rear sight on my LC9 on the first range visit. Evidently, Ruger doesn't tighten adjustable rear sights much out of the factory. My SR22 also was quite loose upon delivery. Never seen a front one do that, but the guys who work at my range say they find quite a few of them.
Yea though I walk through the valley of the shadow of death, I will fear no evil. My rod is a GLOCK and it comforts me