another Victor regulator

I have a set of Victor CGA 540 regs and a Journeyman torch. I got a miller plasma so I have not used the torch much. When I fired it up all was normal then the low side gauge started hitting the peg and releasing at the pop off. It was a fresh oxy. bottle. I am guilty of not always backing off the reg every time but I do SLOWLY open the valve. My question is about the diaphram. Is it always bad? I also heard it could be stuck. Is it possible to rebuild myself? There is not much I have not rebuilt. heavy trk mech 20 years and some oilfield exp. plus I just love to rebuild things. never was smart enough to know I couldnt. but I am not too smart to listen.The welding supplies all said we send em off , 200 dollars we will call you. That may be the case but I dont know. Any help will be appreciated. Thanks