I have a 4 way manifold from Keg Cowboy and found defects in the ball valves. Probably Chinese, the ball valves were two piece where the threads were actually sleeves threaded into the valve body (top and bottom). The sleeves were sealed with some sort of hard glue like substance. Over time, the sealant began to flake and crumble leaving small pinholes. Gas was escaping through the threads.
There was no way for me to remove the sleeve, seal w/tape, and rethread. The valve was machined this way and probably meant for something other than gas under pressure.
It took me a while to find this nonsense. I replaced the valves.