I'm not much liking those guidplates,so for now I'm gonna blame them for this.
It looks like the guideplate either was'nt aligned properly @ set-up,or they may have shifted @ some point during running,and thus they loaded the roller axle unevenly and that caused the axles to fail.
Excessive lash may also be a contributor to that as well.
All/any of the times I've seen that style of guideplate used successfully,they are set-up and aligned first,then they get tack welded in that middle bar to keep them from shifting around afterwards.
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This space for rent...
In the meantime,check out the cars
HERE.