Grease/crud, maybe worn metal would be my guess too. I went back this afternoon looking for the two video's I saw it on, but Utube scrambles the various video's every time you go back on the site. There are unlimited video's. Not getting a real good shot of the ends and when I would 'pause' the video's, the still was to blurry to make out anything, that aroused my curiosity. Some of those video's are pretty good with good explanation, but some of them were crap. Some of those guys don't even know the proper name for parts (calling them a 'thingy'), don't take down or assemble in proper order-guess that is the result of technology, anyone with a modern cellphone or recording device becomes a instant Utube expert. Oh well, thanks for the responses. Didn't think there was ever any 'button' on the end, but ya never know.