As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PASSING THROUGH 15000 FEET WE RECEIVED REVERSE VIDEO LOW ENGINE OIL QUANTITY AT 4 QUARTS. WE RAN QRH AND RETURNED TO PDX. OIL QUANTITY INCREASED TO 6 QUARTS ON DESCENT AND APPROACH. IT THEN DROPPED TO 3 QUARTS ON FINAL APPROACH. OIL TEMP ENTIRE TIME NEVER GOT ABOVE APPROXIMATELY 125DEG C WE DID NOT SHUT THE ENGINE DOWN. GROUNDED - YES. AIR TURNBACK. DIVERSION TIME 14 MINUTES - REMOVED AND REPLACED #1 ENGINE. A/C RELEASED FROM ETOPS RESTRICTION.