Chris,
I've had this rv for 18 years. When I've opened the valve every other time I opened it all the way then turned it 1/8 turn back. Never had a leak or smell. I'm guessing what happened was in this 10 degrees that when I opened it that whatever kind of inner seal it has must have cracked or something. I did try it all the way open & while I didn't hear a hiss I did have a smell. I do not feel safe using this and will try calling some rv shops when they open in 15 minutes.
It is an ASME tank mounted horizontally under the side of my Class B.