The C-clip that holds the spur gear in place is actually a circlip. If you look around and get a pair of circlip pliars they will fit into the two holes on either end of the clip and open it to allow you to remove it and then when you have replaced the spur gear you can open it again to refit it. Im on my third set of spur gears and my second one way bearing but my mt2 is quite old. Strangely though ive never had any problems with the diff cups.