Summer of last year, I did extensive business travel in Canada, and had opportunity to chat with some Canadian Army competitive shooters and armorers, including a seven-time National champion. He is a shooting coach for the Bisley Commonwealth competitive shooting now.
The subject of Norinco M14 rifles came up, and the concensus was "DON'T BOTHER!" Aside from the mentioned heat-treat problems, non-interchangebility with G.I. parts, and the poor quaiity finsh and machining, what more do you want to know?
The price of the Norinco rifles and actions makes them attractive, but in the end, you have to spend a lot more money and time to make them comparable shooters to a more established product.
I've owned Springfield Armory and Smith Enterprises M1A/M14 receivers fitted with GI parts, and must admit to that the pride of ownership of a Genuine Made In The USA article is well worth the price difference! There is an old saying, that you should never buy consumer goods made by workers that are not able or allowed to buy and use those goods. That applies to quality cameras, optics, sports cars, and particularly, to firearms!
HTH
John