pic: Another stripped VexPro gear

[MVCI]

Is the output direct driving a wheel (ie output shaft going through a rigid frame)? Look into the possibility for relative motion between the output gear and its driving gear. This could be caused by loose transmission mounting or flexing of the plastic case. With extra load/impacts on the gears being part of this game and improper gear mesh (caused by relative motion between gears) I imagine this could easily happen.