Derek; I have this lathe and had this exact same problem. Look on the web site. I remember there is a document that details how to fix indexing problems. The hand wheel does unscrew and it is a LEFT HAND THREAD. Lock the indexing if possible. If not, mount a chuck in the head stock and put a bar across the chuck to prevent it from spinning. Mine doesn't have a set screw. You can get a grip on the hand wheel by using the knockout bar for a lever. Insert lever from the front and press the lever down.
While you have the cover off, check for dust in the speed sensor. Gently blow out any dust with compressed air.