As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER CLIMB THE LEFT OIL PRESSURE GRADUAL FELL FROM 100 PSI TO 25 PSI, STAYED THERE AND THEN WENT BACK TO 100 PSI. AIRCRAFT RETURNED TO MSP. ON TAXI IN THE PRESSURE WENT DOWN TO ABOUT 5 PSI. PROP OPERATED NORMALLY AT ALL TIMES. MAINTENANCE REPLACED PROP GEAR BOX OIL TRANSDUCER. OPS CHECK GOOD.