I suspect that one of the shafts is twisted out of phase a little, causing the stress on these outside walkers. We had an MF 850 break a rear shaft this year and upon installing a new shaft, found that two walkers appeared shorter. Unable to stretch them, I slotted the holes and split the difference. This got the guy going, as he was in a hurry, but now his machine has a tight spot in the walkers. How long it will last, I don't know. But I am sure that when the thing jammed, He didn't stop driving untill the shaker pan and shoe were packed full of corn. The rear beater had continued to beat at the front of the walkers, and twisted the shaft out of phase, exactly where the rear one had broken. Two days before he had me disconnect his beeper becuase it was annoying him, and he didn't want to take the time to repair the circuit - Bad move!