I got a set of diamond bits at Ace Hardware for the Dremel tool. One of the bits is an upside down triangle, and there are several ball-ends. Either one works. Run them at the slow speed to limit wear.
Take the wheel adapter (has the screw in the end) and cut yourself a small circle of emory cloth, stick the screw though it. If you put the abrasive towards you you can can stick it in the hole and clean up the inside of the hole. Be careful not to use too big of a circle, or to aggressive paper or you'll scratch the leade.