Kinda wonder if the dogbone just snapped at the thinnest points are these just stamped steel parts? that might be the cause, a small fracture at the weakest areas due to the stamping process. how thick are these dogbones? also could have had some burs from the stamping process which caused heat when the outward pressure is applied on the gears. the dogbones are what keeps the gears in place, rotational forces would create outward pressure and if the bores on the dogbone had any burs from stamping it would create heat along with a possible fracture at the weakest area. I see the pin has a grove cut into it from the damaged dogbone.