As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 4178, THE CREW REPORTED STRONG OIL FUMES POSSIBLY COMING FROM THE NR 1 PACK. THE AIRCRAFT RETURNED TO DEPARTURE, LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE AIRCRAFT AND REMOVED AND REPLACED THE NR 1 ENGINE. OPS CHECKED WITH NO DEFECTS NOTED AND THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.