As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FUEL TANK NR 1 DROPPED FROM 11,600 TO 10,900 ON TWO SUCCESSIVE LEGS WHILE FEEDING ALL ENGINES FROM TANK 2. BALANCE WAS CORRECTED AND REMAINED STABLE WITH X-FEEDS SET TO ENGINE FOR REMAINDER OF THE FLIGHT. *S/D* BROKEN NR 1 TANK VENT TUBE. REPLACED VENT TUBE.