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That is the tough question. Hard, maybe all but impossible, to know why the failure happened.
Not common but not unheard of either.
With less than 20 hours time I suspect the motor is new and under warranty. In which case a new block will be provided. They will remove all of the undamaged parts from your motor and install them on a brand new block. Together with new parts to replace any collaterally damaged parts. The new block, dressed with all of the needed parts, will be installed on your motor.
It is life. Sh1t happens.