As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED MINOR ENGINE SURGING DURING FLIGHT. AFTER TROUBLESHOOTING AND REPAIRS, FOUND TO BE THE ENGINE DRIVEN FUEL PUMP INTERMITTENTLY DROPPING FUEL PRESSURE. ON INVESTIGATION THE OIL SEAL IN THE DIAPHRAGM PUMP WAS FOUND TO BE LEAKING AND OIL WAS IN THE AIRSPACE ABOVE THE DIAPHRAGM AND ALMOST COMPLETELY FILLING ONE SIDE UNDER THE LOWER DIAPHRAGM.