this is not an uncommon problem. usually caused by not torquing the crank bolt to 137 ft. lbs. be ware. some manuals mis-quote this spec.
replace the crank sprocket, pulley, key and maybe the bolt.
you do not have to do anything to the crank it self.
i would also also replace any and all parts related to the timing belt,
belt, all idlers, water pump, and seals. once done you will not have to deal with the crank bolt for 60k - 100k miles.
install the new parts and line up the new crank sprocket. the damage to the crank will let the sprocket ''slop'' in the counter clockwise direction, not the clockwise direction. if you install everything with the correct alignment and torque it to spec, you should be good to go.
the key does not hold the sprocket in place. if it did you would not have this issue. the key only aligns the sprocket while you tighten the bolt. thge bolt dose all the actual ''holding''.
note: not the arrows, never the arrows.