I have always advised against valve stem extensions. Unfortunately because I kept procrastinating I never got around to pulling them off my bus when I got it.
Today I pulled the drive axle outer wheels so I could access the forward air bags. I'm glad I did. The attached photos are of my drive axle, inner wheel valve stem extensions, and one of the wheels showing the hole the extensions go through.
Michelin at one time spoke against extensions because of the fact that eventually the valve stem would fail at the bend due to fatigue from centrifugal force. What they failed to stress was if the valve stem does not fail due to fatigue, the extension would eventually wear a hole in itself and the inner tire would lose its air.