While preparing to work on my wheel hubs (see companion thread http://www.bikeforums.net/showthread...36#post7190436 for more), I figure it would be best to repair my sprocket cassette at the same time. ...but I don't see how it's attached. What holds it on and how do I get it off? Also, the wheel bearing under the cassette may be damaged, as I have lost one of the balls and have had three more fall out. Would my local hobby shop probably have bearings as well?