Snap On MW120 MIG Welder

I am very familiar with this exact welder, as I have used it a good bit in the past. It's welded great with .023, .026, .035 and .045 in the past, all with my own hand. Kirk said he assumed it was the liner because the last time it did this a new one fixed it. I may try a whole new gun on it. Although I cannot see how the sheath of the gun could cause binding in the liner since the liner is coiled steel.