As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) INBOUND, NR 4 PROP RPM DROPPED BELOW LIMIT ACOMPANIED BY RPM FLUCTUATION AND TORQUE ROLL.THE ENGINE WAS SHUTDOWN AS A PRECAUTION. THE AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE NR 4 VALVE HOUSING AND AIRCRAFT WAS RETURNED TO SERVICE.