The mixer was making grinding sounds, and the planetary drive would slip. I completely disassembled the gear box, following directions on the AppliancePartsPros.com YouTube videos, as well as the parts descriptions on the website. The worm follower gear had several teeth damaged or missing, and I also discovered that in a previous rebuild 6-8 years before, the repairer (me) had incorrectly placed the thrust bearing on the rear of the helical gear. I went ahead and replaced all of the gears and bearings, except for the ring gear and two accessory bevel gears, which showed no signs of wear. I did pull, clean and replace the ring gear as someone had forgotten to grease it earlier, so it was gunky, but undamaged. There was some confusion about which was the rear or front helical gear bearing, since both have the same number on the parts diagram. Contrary to the YT video, the most difficult bearing to replace was the planetary bearing sleeve--I had to tap it out. The repair was simple, but messy because of all the grease, but way cheaper than buying a modern and more expensive stand mixer of uncertain quality. The mixer is way quieter than it ever was. Now, my wife can go back to baking her State Fair winning bread!