Also, put some grease on the new spur gear. When you are adjusting the fit of the gear spur to the pinion, put a piece of paper between the two. That should give you the correct spacing and reduce stripping the spur gear. Check it regularly, because it does tend to shift occasionally. Also, the pinion gears don't last forever either. FancyFoam.com has gearboxes and spur gears. They also have really great planes.

Bob