As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EN ROUTE, NR 1 ENGINE OIL QUANTITY INDICATION BEGAN DECREASING. THE FLIGHT RETURNED TO DTW AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE OIL QUANTITY TRANSMITTER AND INDICATOR WITH SERVICEABLE UNITS. OIL QUANTITY SYSTEM OPERATION SATISFACTORY.