What was found
(CAN) UPON APPROCH INTO XXXX, FLIGHT CREW OF C-XXXX ATTEMPTED TO SELECT GEAR DOWN. `LANDING GEAR CONTROL` CIRCUIT BREAKER FOUND TO BE `POPPED`. BREAKER RESET & DOWN SELECTION RE-SELECTED. POSITIVE DOWN LOCK INDICATION FOR BOTH MAINS ACHIEVED, NEGATIVE INDICATION FOR NOSE GEAR FOLLOWED BY CONTROL BREAKER `POPPED` AGAIN. EMERGENCY HAND PUMP EXTENSION PROCEDURE INITIALIZED FOLLOWED SHORTLY BY `HYD FLUID LOW` ANNUNCIATION & THEN FOLLOWED BY POSITIVE NOSE GEAR DOWN LOCK INDICATION. NORMAL LANDING C/O BY FLIGHT CREW. FOLLOWING LANDING MAINTENANCE JACKED A/C & DISCOVERED TWO OF FOUR ATTACHMENT SCREWS FOR THE SELECTOR VALVE TO POWER PACK HAD SHEARED RESULTING IN O-RING FAILURE & SEVERE FLUID LOSS OF THE HYDRAULIC SYSTEM (TC# 20190501023)