What was found
HYD Y RSVR LO LVL IN FLIGHT, QRH, ECAM POSSIBLE SLOW LEAK IN SYS. DID NOT DEPLETE THE SYSTEM, EMERGENCY DECLARED. SERVICED AND PRESSURIZED THE YELLOW SYSTEM IAW 12-12-29. FOUND LEAKAGE AT YELLOW SYSTEM AUTOMATIC SELECTOR 2576GM. R & R THE AUTOMATIC SELECTOR IAW AMM 32-42-13 PB 401.