oldermodelguy
IDK how either but on my Paashe VL the male connector of the quick disconnect that fits onto the airbrush thread the o ring can somehow get turned on edge down inside the airbrush passage. Makes 0 sense to me but the result in my case is an air leak, the brush still works as the ring is skinny and doesn't totally block the passage, just consuming much air.. I might see if maybe I can get a hardware store o ring that will fit in there ( unlikely since my local hardware has a rather small assortment of these.). However, if diligent I have found that I need to be sure the ring is fully down in the nut and fitting the outer groove ( in mine indeed there is a groove there for the ring). I have to take a tool and kind of pack the ring down in there. As it turns out the stem of the metal paint cup fits perfectly to seat that ring.Then lube the male thread with lip balm and assemble it, you can almost feel the male portion slip into the O ring then as it's lightly seated.
OMG - The city near me is not all that big, but there are two great sources of air fittings and "O" rings there. One specializes in pneumatic everything, the other carries only O rings, any O ring I've ever needed they have.
Check your phone book or a Google search in your area, you might be surprised at sources available.