Unlike engine oil, gear oil takes a great deal of heat, without breaking down. It is used in gear boxes or differentials where pressures in interlocking metals are more extreme. Proper oil levels and viscosity are needed for maximum operation of your rotating machinery.
A "C-Face" motor is a common American mechanical standard designed with a rugged flange on the face of the motor for mounting purposes. The weight of the motor is supported by the flange, which is most commonly attached to a gearbox. The flange is strong enough to cantilever the motor.