Trackmaster belt drive for monster beetle
I've just taken one of these apart and I also found the diff to be difficult to dismantle. I heated it up with a gas torch and found that the diff had been glued together with epoxy. The diff screw was broken and the thrust/diff bearings were missing. If the diff screw was a weak point in the design, then yours may have hte same problem. Click the link on my profile page to see pics of my trackmaster ...