Hi Debbie - After carefully analyzing the schemeatics for the mixer it became clear that the planetary assembly is not supposed to detach from the main shaft in that way, and there does not appear to be a clear fix - I'm not sure how it stays on - must be friction.
The good news is that I was able to buy a new planetary assembly complete with shaft for less than $20.
Installing it was not overly complicated, though you need to remove a tension ring with tension ring pliers to get it off. I needed to get a new ring form the hardware store to reassemble it.
I found a repair guide for the mixer online which was helpful.
If you aren't good at this type of thing, I bet you could find someone to do it for you pretty easily - the whole fix took maybe 30 minutes, but you are opening up the mixer, so need to be confident.
Hope this helps!
Last edited by skixc : 02-17-2012 at 11:46 AM.