I changed three gears on three bad oscillating motors today. Took less than 10 minutes on each. Took 3 screws out with an impact wrench. Push out the old gear. Clean the brass debris from the inside and put everything back in reverse. The smooth edge of the gear goes downward. Add gear oil and tighten screws back up. This was easy. I regret throwing away so many reusable oscillating motors over the years.