I had my K-1000 in my backpack most of the day yesterday, and when I pulled it out today I heard a weird rattling sound. I took off the lens and the middle component on the back end of the lens had fallen out. I managed to put it back in and get it to stay by turning it—as far as I can tell, this piece does not attach by threading, but that's sort of how I treated it—and it seems like it's staying put, but I notice there is still a bit of a rattling sound, which doesn't happen with my other lenses. I'm wondering if there's an easy way to secure this piece without taking it in for repair, or whether a little bit of rattling is no big deal. Any tips appreciated.