My experience, for what it's worth, is that once the valves get to the point you described the only fix worth doing is to replace them.
As already indicated, the replacement valves are surprisingly inexpensive. Replacing them isn't overly difficult, and you can minimize the mess by extending the jacks on the passenger side of the coach, draining the tanks, retracting the passenger side jacks, and extending the driver's side jacks before removing the old valves.
Another useful tip is to replace the nuts on the bolts that hold the valves in place with nyloc nuts. The nyloc nuts will allow you to tighten the nuts & bolts just enough to prevent any leaks but not so tight as to damage anything.
For more detail on the valves themselves, see my post & photos on page two of this thread:
http://www.irv2.com/forums/f278/repl...es-425882.html