The ABS plastic wasn't the stupid idea, I don't think. The screws are what caused this. Instead of only creating downward pressure, the screw heads create downward and outward pressure, basically forcing the arm to separate where it has. The tighter the screw is, the more outward pressure it creates, spreading the hole. You can see from the pics that they split from the top down.

I don't think this had to do with rough running, but rather turning the screws down too hard. I had taken the arms off a while back and may have overtightened them on that side. At least that's what I'm hoping. It would be a shame that the same use I have dished out to the King Tiger was too much for the "Uber" Tamiya.