As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1 ENGINE OIL QUANTITY WAS DECREASING IN FLIGHT, ENGINE WAS RETARDED TO IDLE POWER. THE FLIGHT RETURNED TO MSP AND LANDED WITHOUT INCIDENT. OIL LOSS WAS CAUSED BY A DAMAGED OIL CAP SEAL. MAINTENANCE REPLACED THE OIL CAP O-RING AND RAN THE ENGINE TO CHECK FOR LEAKS, NO LEAKS NOTED.