As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE ROTOR SHAFT WAS FOUND BROKEN IN TWO. THE BREAK LINE INDICATES A CRACK WAS PRESENT FOR SOME TIME PRIOR TO SEPARATION. THE MAG AHD NOT HAD ANY INTERNAL MX. 2 WEEKS PRIOR TO THIS, THIS SAME ROTOR BREAK OCCURED ON A 4370 WITH 708 HOURS TIME IN SERVICE.