| My dad just experiance this issue on his garage door recently. You can get the new parts from Sears and replace the gear and sprocket. Average hand tools, (don't need a torch or a welder)lol to do this. The parts took about a week to get and total time replacing it was about an hour start to finish. Price for the parts was far more economical than replacing the unit. Be sure to unplug the unit before servicing and oil/grease the track the chain travels on as well as the door rollers and tracks. Good luck | 
