What was found
(CAN) DURING FLIGHT THE ENGINE OIL PRESSURE INDICATION DROPPED TO 20 PSI, THERE WAS NO PROPELLER RPM CHANGE AND NO LOW OIL PRESSURE WARNING LIGHT. A PRECAUTIONARY SHUTDOWN WAS CARRIED OUT AND THE AIRCRAFT RETURNED TO BASE. THE OIL PRESSURE WAS CONFRIMED WITH A DIRECT READING GAUGE AND THE OIL PRESSURE TRANSMITTER WAS DETERMINED TO BE THE FAULT. THE UNIT WAS REPLACED AND THE AIRCRAFT RETURNED TO SERVICE.