equipment gurus: i bought a 2 stage reg with 3 fabco nv 55 attached. i was only planning to use 2 of the NV and so did the previous owner. so in the possession of the previous owner, it was closed all the way as a shutoff, while the other 2 ran. problem is the nylon knob is free spinning now and i cannot adjust co2. since then, i took that problem NV out and plugged the manifold with a 1/8th plug. i tried tightening the 2 allen screws in the problem nv but cannot get it to stop freespinning. it will turn and turn and never have enough resistance to actually stop turning into a closed position. im not going to use it closed but want it to function properly. is it salvageable?