I weld infrequently so I wondered how I could go so quickly through a
160 cf bottle of argon. Turns out my Dynasty 200 DX had a leak at the brass argon fitting at the back of the welder, not at the hose connections but between the fittings themselves.I heard the leak when I was setting the machine up (after I hooked up the argon but before I turned the machine on). Later after the welder was unplugged and idle for a while I confirmed the location with a soapy water test.
The Miller engineer confirmed that there was a manufacturing defect (that they found quite a while ago) that made the female socket slightly out of round. He immediately offered to send me a new fitting for free. I was able to install it myself --it's held there by just a c-ring clip. I installed it just this morning and the symptoms are gone.
I think another sign that you might have this problem is the wear mark on the fitting. Look into the conical receiving area. (The front and back gas fittings look, and probably are, the same.) The good fitting at the front shows a continuous circular mark where the male fitting makes contact. The bad fitting at the back shows this same circular mark, except the circle is broken into 4 or 5 segments. I guess this is where the gas was getting thru.
--zeb