My new (to me) mid 90's Gretsch came with a Pratt Muffler and I can't figure out how to get it to function properly. I was told to loosen the knob and then play, and it would slowly adjust, but it doesn't seem to be happening. When I had the front head off I checked it and I had to pull the muffle away from the head by hand.

Any ideas? Does it just need to be lubed possibly or is this just how they all are?