footvalve help

The truck is a 78 kW cab over. I don't think that part matters lol. But the footvalve is leaking out of the exhaust. Doesn't matter if the yellow button is in or out. It also has the mysterious blue knob, but same goes for that. There is a bunch of moisture in the tanks. Could it be that it has passed that moisture through the valve and gummed up the exhaust plunger and is not seating correctly? But I was under the understanding that the footvalve shouldn't have pressure to it until thevdash valves are pushed in. Maybe I'm wrong there, but it still leaks and would like to know why/what to replace. Also, with buttons in or out and brake pedal applied, air comes out of the service/blue trailer line. Thanks for any help!