What was found
(CAN) AFTER DEPARTURE, CREW UNABLE TO RETRACT ALL GEAR. NOISE HEARD FROM MAIN LANDING GEAR. AIRCRAFT DIVERTING BACK TO DEPARTURE AIRPORT AFTER BURNING OFF FUEL DUE MAX LANDING WEIGHT COMPROMISED. RESOLUTION FOUND DAMAGED, LEAKING SEAL AT NLG SHOCK ABSORBER PREUMATIC SERVICING VALVE. REPLACED VALVE AND SEAL. ADJUSTED NLG SERVICING CHARGE IAW AMM 12-12-32-610-001-A01. PERFORMED NLG EXTENSION, RETRACTION FUNCTION TEST IAW AMMM 32-31-00-720-003-A.