To maybe fix the leak, try checking the ends of the air tubes, and see if they're cut straight. If they've been cut at an angle, they can leak. Cutting them straight should fix it. Note that this may not be the issue, but it's a simple thing to check before you disassemble the whole pneumatics system. Just make sure to vent any air in the tank before working on anything!
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"You know, it's amazing how many things you can take apart with just one ordinary screwdriver!" - Calvin, from Calvin and Hobbes
"There's nothing a little duct tape and surgical tubing can't accomplish." - Sheldon J. Plankton