What was found
CREW REPORTED THAT GEAR RETRACTION, LANDING GEAR WARNING HORN SOUNDED AND ALL THREE GEAR DOWN ANDM LOCKED LIGHTS REMAINED ILLUMINATED. TOWER FLY-BY REVEALED THAT GEAR DID NOT LOOK "NORMAL". CREW PERFORMED "GEAR WILL NOT EXTEND HYDRAULICALLY" PROCEDURE USING EMERGENCY EXTENSION SYSTEM. SECONG FLY-BY REVEALED GEAR STILL DID NOT LOOK " NORMAL". CREW DECLARED EMERGENCY, LANDIND WAS UNEVENTFUL. MAINTENANCE FOUND LEFT MAIN LANDING GEAR STRUT FLAT. MAINTENANCE REMOVED REPLACED UPPER TRUNNION O-RING. SERVICED STRUT, PERFORMED GEAR RETRACTION AND EXTENSION TEST, SYSTEM CHECKED OK. AIRCRAFT RELEASED BACK TO SERVICE.