What was found
(CAN) IN CRUISE PASSENGERS REPORTED FLUID COMING FROM LT WING. F/O VISUALLY CHECKED AND REPORTED LT WING, SOAKED. RT WING DRY. FUEL DISCREPENCY OF 400 DECIDED TO RETURN TO DEPARTED STA. LT WING THOROUGHLY CHECKED FOR SIGN OF FUEL LEAK OR PATCH OR ODOR. UNABLE TO FIND ANY PROBLEM. FLUID ON WING WAS DE-ICING FLUID, AFTER REFUELED TANK DRIP CHECKED AND CONFIRMED READING WITH COCKPIT INDICATIONS. LOW PRESSURE CHECKED BY RUNNING PUMPS NO LEAKS.