I had that happen on my F540 this year because I lost the bolt out of the cam adjuster and my local tech told me that some headers break at the weld inside the auger and its not an easy fix. Mine was just put in new fingers and a new bolt in the adjuster...guess I got lucky.

 

This has happened to my both of my 1200 maxflex heads three times now. When the fingers fully extent it tears the tin off the front of the feeder house just before all the fingers shear off. Even if you hit the stop button when you hear the shaft break, the momentum is still going and you just sit ther watching it tear the tin out and spit fingers out the front on the ground�� I've never had this happen on my f30s or my f535s or my f540s. I noticed that the hole in the cam the shaft goes into is off 1/8" from center of the cam on my maxflex 1200s. I think this might cause it to constantly flex breaking out welds. I think something may have been off at factory.