What was found
(CAN) FLIGHT CREW REPORTED YELLOW & BLUE HYDRAULIC SYS FAILURE, HAVING FLIGHT CONTROL DIFFICULTIES. EMERGENCY WAS DECLARED, ARFF MET ACFT ON ARRIVAL. HOT BRAKES REPORTED IN CRUISE "HYD Y RSVR LOW LEVEL" ECAM ACTIONS CARRIED OUT. WHEN PTU SEL. OFF PTU CONTINUED TO RUN. IN CONSULT WITH MOC C/B N34 PULLED. NO FIX Q36 & Q37 PULLED, THEN PTU STOPPED. FOUND O-RING LEAKING ON PTU MANIFOLD. REPLACED O-RING AND CHECKED FOR LEAKS. FUNCTION AND OPERATION OF EDP CARRIED OUT IAW AMM 29-11-00-710-001A . YELLOW SYS ENGINE 2 CASE DRAIN FILTER INSPECTED NIL FAULTS IAW AMM 29-11-43-301 COWLS CLOSED. FOUND PTU RUNS WITH SELECTOR SWITCH IN OFF POSITION. REPLACED PTU AUTO/OFF, PB SWITCH IAW ESPM 20-45-11. OPERATED PTU IAW AMM 29-23-00, PB501 SEVERAL TIMES, CHECKED SERVICEABLE.