It's a Clippard Minimatic pneumatic valve. It works like a Norgren valve. Here's where to find them:
http://clippard.com/store/display.as...=6002&levels=1
I've never seen them, and I don't know what they do on your bus. If you want to try and fix it, drain your air down, then try taking the two screws on the bottom of the valve out, remove the valve, get the part number off of it, clean any crud on it off, then reinstall it and see if it still leaks. If it leaks you have a part number and can then get a new one - depending on the part number they run between $20 and $50. There's a manifold underneath that the valves plug into - that may be cracked and leaking, or the airlines going in could leak as well - the manifold might look like this -
http://www.clippard.com/store/displa...asp?sku=CM-036
Get your soapy water ready - Hope this helps Steve