As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE OIL PRESSURE WAS FLUCTUATING DURING CRUISE. ENGINE WAS SHUTDOWN AS A PRECAUTIONARY MEASURE. AIRCRAFT RETURNED TO DEPARTURE. FOUND RT ENGINE OIL TANK FILLER CAP O-RING TORN. OIL LEVEL WAS DOWN 2.5 QTS. REPLACED O-RING WITH NEW, SERVICED ENGINE OIL WITH 2.5QTS. PERFORMED ENGINE RUN UP, LEAKAGE CHECK, AND OIL PRESSURE CHECKS MM.