The belt on my Jet blew last week, and the speed control has been sticky lately. So I pulled the entire drive and quill apart, cleaned/lubed it, and installed a new belt. Runs better than ever. Jet says this is a factory service, but I can help anyone who wants to do it themselves. Not too difficult, and no special tools needed.
One interesting thing is that I was able to pick up the replacement vee-belt at NAPA for a fraction of the Jet price.