As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE RIGHT ENGINE OIL PRESSURE DROPPED INTO THE YELLOW ARC DURING FLIGHT. THE AIRCRAFT MADE A PRECAUTIONARY LANDING (DID NOT SHUT DOWN ENGINE). INVESTIGATION REVEALED THE SPRING BROKE IN THE STARTER ADAPTER AND PIECES BECAME LODGED UNDER THE RELEIF VALVE. THE START ADAPTER WAS REPLACED. FLUSHED OIL SYSTEM, OPENED FILTER AFTER GROUND RUN FOR 30 MINUTES. NO METAL NOTED IN FILTER.