As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON REACHING CRUISE ALTITUDE THE LEFT OIL PRESSURE GAUGE BEGAN TO FLUCTUATE WILDLY FROM ZERO UP TO MAXIMUM PSI. NO LOW OIL PRESSURE ANNUNCIATOR WAS OBSERVED AND ALL OTHER ENGINE PARAMETERS WERE NORMAL. THE AIRCRAFT RETURNED TO HOME BASE WHERE AN UNEVENTFUL LANDING WAS MADE. INVESTIGATION REVEALED A FAULTY OIL PRESSURE TRANSDUCER. THE TRANSDUCER WAS REPLACED AND GROUND OPERATIONAL CHECKS AT ALL POWER SETTINGS WERE SATISFACTORY. THE AIRCRAFT WAS RETURNED TO SERVICE.