Take off your front block and push something long and thin into the hole where the front block screw goes. Push hard enough, and the valve will come out. I've done that with a couple stuck valves on my various cockers. I use this long metal rod that I found in my garage, you should be able to find something that'll work. Needs to be something thin enough to fit through the hole, long enough to reach the valve, and hard enough not to bend.