[Richard]

Can you access the rear six pack? Tee into the supply line to the six pack. Inflate that with your home compressor. Or access any other convenient spot. Have you tried the air hose connection at the rear for use as an input point? Pressuring the distribution valve from the supply side just may unstick it. Let me know if this brief explanation typed on my phone doesn't make sense

If you pressurize the six pack. You'll have to use the manual up buttons to get air into the air bags