My KitchenAid Professional Series 6 mixer which is about 20 years old suddenly stopped working. The motor would run but the beater would not complete a full circle without a push from me. I took the gearbox apart to figure out why the beater would not turn and discovered that the worm follower gear had most of the teeth stripped from it. I believe this was caused by a lack of grease. As I removed the gearbox cover, I noticed that most all the grease had been thrown to one side of the gearbox. Very little grease was on the gears themselves. Some research lead me to AppliancePartsPros.com website and the very helpful videos. I ordered the gear and grease, then disassembled and thoroughly cleaned all the parts as instructed in the video. I also found flour and sugar in the On/Off slide control which had not been working smoothly for quite some time and took that apart and cleaned it up also. When the gear and grease arrived, I partially assembled the gearbox without grease and manually tested (no electrical power) to make sure everything worked properly. I disassembled and started again using the grease as instructed in the video. About an hour later,I had everything back together except for the cover. I ran the mixer for about 15 minutes at various speeds, then opened the gearbox to check that all the gears were still covered with grease. They were not. I added more grease, closed the gearbox, and ran the mixer again. I opened the gearbox again the grease covered all the gears. The mixer is now working great. Hopefully, I can get another 20 years out of it. Thank you AppliancePartsPros.com.