$10.95
This is identified as part # 37 in the exploded parts diagram
Please note, a common issue with the toy train locomotives, is that gearbox covers break where the screws go through the top cover to hold the cover and motor in place, this will invariably cause pre-mature ware on the drive gears. it is recommended to check the top cover when replacing the gears
please review this documentation about the different Toy Train/Porters to ensure the correct gears
