As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) MAIN ROTOR RPM WAS FOUND TO OSCILLATE DURING CRUISE FLIGHT AND SOMETIMES DROOP DOWN -5 RPM NR. REPLACING FUEL CONTROL UNIT, FUEL PUMP AND GOVERNOR DID NOT HELP THE PROBLEM. REPLACING THE OVERSPEED GOVERNOR ELIMINATED ALL SYMPTOMS.