If the brush does not want to rotate and it is already cleaned of all hair slacks and the contacts are intact, there is another possibility. Connect a charger for the car battery to the contacts of the motor head and see if it works. If it works, then the control unit measures too high an initial current. You can check this by inserting a thin wire about three meters long into the circuit. The resistance of the wire should be about 3-5 ohms. To do this, you need two cables with terminals. Output motor to input brush, output brush to thin wire to input motor or vice versa. Now the current is limited and it should start. However, the wire gets warm and the brush does not rotate as fast. If you are skilled in craftsmanship, then you order a thermistor such as cl-160 from Farnell (5 Ohm, 11.5 J, 2.8 A, costs some cents) and solder it in the motor head between one of the cables connected to the engine. In this way, I made two brushes rotate again. Good luck.