The transmission gear split apart. This damaged the gears it meshed with above and the gears it meshed with below(in the rotor assembly). So, I had to replace all 3 sets of plastic gears. The top gears cost $26. The transmission gears cost $10. The bottom gears cost $108, because they are only sold in this full assembly which is about 24" in diameter with magnets all the way around. When I got the assembly it was damaged. About 1/2 of the magnets were cracked. Luckily, I only needed the plastic gears. So, I took the gears out and installed them in my old rotor assembly and it worked fine.