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Hard to tell root cause on rotating shafts. The broken parts rub together and this often destroys much of the evidence.
One does look like high torque based upon the 45 degree failure. The other could be stress concentration due to a small radius at the transition between the shaft and gear. However type of material or heat treatment could also be a cause.
Since your trans can hold each gear, this may have contributed to the failure but not the root cause. Suggest you let the auto do it's own shifting for a while.
Lee
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