Troy, When you open the valve, do you open it all the way? Partially -opened valves can leak.
 
The thing you are callng he control valve is the regulator and if you hear it hissing it's failing and should be replaced, or else you may have a loosed fitting.
 
You can find where the leak is by spraying with soapy water and watch for bubbles. 
 
Meanwhile, keep the on-off valve completely closed when not in use.
 
Robert
1982 Westfalia
 
 
 
 

--- On Sun, 6/8/08, Troy <colorworks@GCI.NET> wrote:

From: Troy <colorworks@GCI.NET>
Subject: propane valve leak
To: vanagon@GERRY.VANAGON.COM
Date: Sunday, June 8, 2008, 5:15 PM

If I recall correctly, someone wrote in maybe about a month ago, perhaps it was
a little bit longer about their propane valve leaking. When I went out to the
garage this morning I could smell propane. Tightening my fingers around the
blue plastic cover of the control valve changed the pitch of a small hiss I was
hearing. This seems to be a somewhat intermittent problem. Underneath that blue
plastic cover of the valve I thought was a pressure release valve. I recently
had a fill up, and have not used any appreciable amount of propane. Is it
possible the tank was just overfilled? I just had a leak not too long ago
around the same valve, had to drain the tank and reappply telfon paste and
refill, so this is getting old. Any advise here? Do I need a new valve?

Troy