[Graham]

It was not quite as drastic as it sounds, the car with the chassis in question was a 3d printed one and the motor was held with a 3d motor holder where it cracked across the grain of the printed surface. I have seen similar 3d parts fail before. And on the other car the guide holder was scratchbuilt with a brass piece glued onto a plastic part, probably not the most robust of constructions. So in both cases the car parts in my opinion was of vulnerable construction.