I replaced both front & rear sleeve bearings along with the shaft bearing to improve stability of rotation of all gears.
I also found the vertical shaft bearing had worked itself out of the housing and was sitting on top of the bevel gear rather than pressed into housing. I reinstalled the vertical shaft TOP bearing into the housing and "pressed" it in with a hammer and socket extension.
I then cleaned all parts and the housing and installed new grease into the proper places.
Upon reassembly, the machine was run at slow speed to ensure all things meshed properly. The machine was then run at top speed for 5 minutes without issue.
I would have 'bought" more parts, like vertical shaft and planetary gears BUT the prices are too expensive and a 'refurbished' unit can be purchased from KitchenAid with a warranty for far less than the parts cost!
Being a manufacturing engineer, it is sad to see the 'mark-up' on piece parts as it tends to make repair unreasonable and wastes a lot of good material into the landfill!
Thanks for working to keep the prices reasonable and hopefully, dropping the price will create MORE repair business rather than throwing away the old to buy new or refurbished systems.