What was found
THE NOSE GEAR RED UNSAFE LIGHT WOULD NOT EXTINGUISH AFTER GEAR RETRACTION. CYCLING THE GEAR PRODUCED NO CHANGE. THE AIRCRAFT WAS RETURNED TO SFO WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE NOSE STRUT FLAT. THE SHRADER VALVE WAS REPLACED AND THE NLG WAS SERVICED WITH NITROGEN IAW MM 32-21-02. A NOSE GEAR SWING WAS PERFORMED AND OPERATION CHECKED GOOD.