I would tend to think you'd be better off to find a gunsmith who specializes in those types of weapons. AZEX in Mesa, AZ comes to mind. I would think they could replace the barrel etc a lot quicker and cheaper then sending it off to Norinco.
The only exception I would guess is IF Norinco has a "service center" or a "contractor" they send it off to here in the U.S.
I once had an M1icon Garrand (a refurb) from Arlington Armory that had problems. They told me to send it off to Brownells in Montezuma, IA as they did their "warranty work"
HTH
Bob