My old '57 Conn 18B Coprion needs a new guide on the 2nd piston. The guide is a small rectangular nylon tab that is either screwed into or pressed onto the piston. The leading edge is deteriorated and is able to be depressed past the value guide groove's end. This causes the piston to stick. I've gotten around the problem by padding the finger button so the piston can not be depressed all the way down. Are there replacement parts available? What about soldering on a tab made of brass? Any info or suggestions would be appreciated.