What was found
(CAN) DURING THE TAXI OUT, CREW RECEIVED A 1 RUD HYD CAUTION LIGHT AND OBSERVED AN ABNORMAL LOW OIL QUANTITY ON THE ASSOCIATED SYSTEM GAUGE. CREW ELECTED TO RETURN TO THE GATE. MAINTENANCE WAS CALLED AND AN HYDRAULIC LEAK NOTICED UNDER THE LEFT WING. FURTHER INVESTIGATION REVEALED THE INBOARD FLIGHT SPOILER ACTUATOR CASING HAD FRACTURED. THE SPOILER ACTUATOR WAS REPLACED, RIGGED, TESTED, LEAK CHECKED AND THE ACFT RELEASED FOR SERVICE.