As Joe says the same also goes with Chinese copper. A friend of mine has designed, built and installed commercial HVAC systems and large custom freezers for over 30 years. He said with some of the Chinese made products you could see refrigerant leaking out as soon as you started using them. He said it was most commonly seen at bends and any joints but could be anywhere. There was a sealant product (developed in the USA) he used and for a while the problem was so bad he carried boxes of it with him all the time.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end