As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOW OIL PRESSURE INDICATION DURING CRUISE FLIGHT AT FL210 APPROXIMATELY 15 MINUTES AFTER TAKEOFF. QRH CHECKLIST COMPLETED. N2 REDUCED TO <80% AS PER QRH. OIL PRESSURE INDICATED IN NORMAL RANGE. EMERGENCY DECLARED AND ELECTED TO RETURN TO DEPARTURE. OIL PRESSURE REMAINED IN NORMAL GREEN RANGE FOR REMAINDER OF FLIGHT. DURING POST FLIGHT INSPECTION, FOUND OIL CAP NOT INSTALLED.