You don't mention the style of extensions that came on your coach.
I've had four coaches (three different brands) and found that the metal ones are less likely to leak, although these things are made cheaply. Like a garden hose, they need to be tight but not over tight where is deforms the seal.
A couple years ago I had a slow leak on an inside dual and went to a truck tire center replace the extension. Just in case the main valve had a problem, he recommend doing a new valve while the tire was pulled off. Not sure which was really leaking, but it holds well now.
Craig and Susan
Morgan Hill, CA 2007 Newmar Kountry Star 3910 towing a 1998 Ford Explorer. RVing since gas was 58 cents a gallon. Amateur Radio Operator (W6ADV) since 1962.