I took the plunge and worked on my valves when they were stuck. Check out the link below and jump in. Four screws should allow you access to the inner workings and I understand that repair kits are available. I just needed to clean them out and replace the gaskets due to damage during dissassembly. You should be able to repair them yourself. Let me know how it goes.
http://www.airforums.com/forum...&threadid=1965