What was found
WHILE THE AIRPLANE WAS OUT OF SERVICE (GROUNDED) AND THE LEFT AFT FUEL BOOST PUMP IN THE LEFT WING WAS BEING REMOVED, FUEL STARTED TO FLOW OUT OF THE FUEL TANK. THE PUMP COULD NOT BE RE-INSERTED UNTIL THE FUEL STOPPED FLOWING OUT OF THE TANK. AFTER THE FUEL WAS CLEANED OFF THE RAMP BY HAZMAT TECHNICIANS, A SERVICEABLE LEFT AFT FUEL BOOST PUMP WAS INSTALLED. THE CAUSE OF THE FUEL SPILL WAS AN UNSEATED FUEL BOOST PUMP SHUTOFF SLEEVE.