[Richard and Rhonda]

Ron,

My coach, and others I have looked at used a Ridewell leveling valve. Ridewell has superseded that design with a new design called Extreme Air http://www.ridewellcorp.com/Web/Site.nsf/ID/air
When I look at the new design, I am not sure if it is a direct drop in or not. Some fabrication may be required as the air in and out appears to be in a different place than the original valves

I haven't looked very hard on the net for a source. I do have a leaking valve, courtesy of my alignment "mechanic", so I am looking to replace the two rear ones.

I have also looked into King of the Road, since they are all metal. Most of the buses run them. http://www.heightcontrolvalve.com/ This may require fabrication of a bracket.

There is nothing special about the leveling valves. Well except you have to be a contortionist to replace the rear ones with the wheels still on the coach.