Befang 1000 Watt Motor

At high toque levels I have notice that the gears in the motor are slipping. At first I thought it was the de-reailers, but I took it to my local e-bike repair shop who pointed out that is was the internal gears in the motor that were slipping. Has anyone else had this problem and if so how can it be fixed. My local bike repair shop said the motor was defective and needed to replaced.