As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE LOST OIL PRESSURE IN CRUISE FLIGHT. THE PILOT MADE AN UNSCHEDULED LANDING. INVESTIGATION REVEALED THAT THE OIL FILLER CAP HAD COME OFF AND THE ENGINE LOST OIL. THE INTERNAL AREA OF THE OIL FILLER TUBE HAD WORN AND WOULD NO LONGER PUT SUFFICIENT PRESSURE ON THE OIL CAP RETAINING SPRING CLIPS. DUE TO THE IMPACT ON SAFETY, THE OIL FILLER TUBE SHOULD BE REPLACED AT ENGINE TBO.