Did you check the mesh before starting it? A spur gear isn't worth sending it back to HPI. A new one will only cost a couple bucks. There are a few things you must do to any new nitro RC before starting it.

1) Check the mesh
2) Check for loose nuts, bolts and screws
3) Check the factory carb settings

I also seal the motor, oil the filter, add a failsafe, add a hump pack and add a charge port before ever starting it. But you can skip these steps for break-in.