What was found
THE LANDING GEAR WOULD NOT RETRACT AFTER TAKEOFF FROM IAH. THE GEAR REMAINED DOWN WITH THREE GREEN INDICATIONS AND THE AIRCRAFT WAS RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE NLG SCHRADER VALVE O-RING CUT AND NLG STRUT DEFLATED. THE O-RING WAS REPLACED AND THE NLG WAS SERVICED IAW MM 32-21-02. A NOSE GEAR SWING WAS PERFORMED IAW MM 32-30-00 AND OPERATION CHECKED GOOD.