I have a Lawnboy self propelled push mower approximately 8 years old. My self propelled feature started making some noises last week while it was engaged in self propelled. I figured it was either a bad belt or gear. It finally went out and last weekend I was able to take the gear box apart. One of the gears that transfers power to the wheels has a portion where the teeth are worn and that seems to be the problem. Here's my question. Does anyone know if replacement gears are available or if I have to buy a new gear box?