As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE ACFT RETURNED SHORTLY AFTER TAKEOFF WITH THE PILOT REPORTING NO TRANSMISSION OIL PRESSURE OR ROTOR TACH READING. FAILURE OF THE XMSN OIL PUMP WAS SUSPECTED. UPON REMOVAL OF THE PUMP, A CHUNK OF A TOOTH FROM THE RING GEAR ASSY WAS FOUND IN THE XMSN SUMP. THE XMSN WAS SENT BACK TO THE MFG FOR REPAIR. THE MFG INFORMED CUSTOMER THEY WERE AWARE OF THIS PROBLEM OCCURRING WITH THESE RING GEARS.