What was found
AIRCRAFT RETURN TO PLATFORM DURING TAXI, CREW SELECTED SLATS EXTEND AND THE HYDRAULIC QUANTITY LIGHT TURNED ON. MAINTENANCE DETECTED HYDRAULIC LEAK IN RT SYSTEM AND QUANTITY ZERO, SO THE SYSTEM WAS SERVICED AND HYDRAULIC PRESSURE WAS APPLIED AND THE LEAK WAS LOCATED AT THE RUDDER SHUTOFF VALVE, THIS VALVE WAS REPLACED IAW MM 27-20-09 TESTED CORRECT, ADDITIONALLY, WATER SEPARATORS OF BOTH AIR CONDITIONED PACKAGES WERE REPLACED IAW MM 21-20-02, TESTED CORRECT.