What was found
APPROXIMATELY 3 HOURS INTO FLIGHT, FL 340, RECEIVED A LEVEL 2 FUEL QTY/USED CHK. COMPLIED WITH QRH. WHEN SYSTEM WAS SWITCHED TO MANUAL AND THE TAIL TANK WAS ISOLATED, THE TAIL TANK CONTINUED TO DECREASE 400LBS IN 4 MINUTES. SUSPECT THE FUEL LEAK WAS IN OR CONNECTED TO THE TAIL TANK. EMERGENCY CREW SAW A SLOW DRIP FROM THE LEFT SIDE OF THE TAIL. THE FUEL DIFFERENTIAL AT BLOCK IN WAS 14,280LBS. REMOVED, REPLACED AND OPS CHECKED BOTH LH AND RH TAIL TANK FULL FLOAT SWITCHES REF FEDEX MD-11 AMM 28-14-01-4. OPS CHECK GOOD