JD 4420 taking out top pulley bearing of vaiable feederhouse

It now appears that the bearing inside of the top pulley of the feeder house variable speed is going out because something is wrong. As stated in the subject line this is a late model John Deere 4420. I replaced this sealed ball bearing in 2010, 2011, and again in 2013. Now it is worn out from the 2014 harvest. So that everyone knows the exact location, this bearing is located inside the pulley (inside a bolt-in hub). This pulley is the top variable speed pulley that slides onto a stub shaft. The stub shaft would be exactly at the pivot point of the feeder house and the combine. This bearing supports the back half of the pulley. There are some other bearings in this variable pulley assembly as well, but they never seem to wear out. From the top of my head I think there is another sealed ball bearing on the front side and a open roller bearing inside. When the bearing goes out it lets the entire pulley move inward towards the side of the combine. Eventually the pulley starts to wear through a plate covering some electrical wires and the brake lines. Why is this bearing repeatedly going out??? Could it be that the stub shaft the roller bearing rides on is worn some allowing the entire variable speed assembly to do a high speed shake putting additional pressure on the subject bearing??? You can see some wear on the shaft. What other things could be causing this?? The belts are not too tight. The replacement bearings were John Deere. I would like to see this bearing last. Thanks.

Is it possible the feederhouse frame is bent somewhere, causing the top pulley to run out of alignment with the other parts of the variable speed drive components? Or maybe the short shaft is bent? Is there unequal tension on the belts driving and being driven by that part that you keep having to put bearings in? I replaced the bearings in the fixed drive pulley hub in the same place on our 4420 last year. Just some ideas... Good Luck!
Lon