What was found
CLIMBING FROM 380 TO FL400, "HYD VOL A" CAS MESSAGE CAME ON. HYD VOL A WAS 13 PERCENT. FOLLOWED THE CHECKLIST, UNLOAD HYD PUMP A AND PULLED B/PTU CB. DIVERTED, DECLARED EMERGENCY, BLEW DOWN THE LANDING GEAR. ABOUT 15 MINUTES LATER THE HYD VOL A WENT TO 43 PERCENT, LANDED UNEVENTFULLY. USED THE EMERGENCY BRAKE AND WE WERE TOWED TO MFG. REMOVED AND REPLACED THE LT HYD RESERVOIR IAW THE MM 29-10-01. LEAK AND OPS CHECK NORMAL. REPLACED UNION FITTING, O-RING ON THE HYD "A" ACCUMULATOR WITH NEW PN: NAS1612-8, DUE TO LEAKAGE. LEAK AND OPS CHECK NORMAL, IAW THE MM 29-10-01. COMPLETED HYD SYS AND BRAKE BLEEDING IAW THE MM 32-42-00 AND 29-10-01, 12-10-15.