So last night, I took apart the gun for it's routine cleaning, which I haven't done in a few months. I take the slide off as usual, unscrew the guide rod, and set the pieces on my work cloth. I get up to go get my silicone oil, and when I come back, I see a tiny metal ring sitting on my chair. I don't mean bushing thick, it's almost paper thin. I don't ever recall seeing it in/around the pistol before. When I finished oiling as usual, I put the gun back together as usual, and I didn't see anything that stood out to be missing. So...I'm sort of wondering if it fell out of something when I was taking the slide apart...or if my chair is falling apart.
If it IS a part from the gun, my best guess is that it's some sort of buffer between the spring and the rubber bit on the end of the guide rod. It doesn't seem to fit anywhere else.