I guess I should have given more information about my setup... Like a
previous poster, I have a ball valve shutoff coming straight out of
the outlet from the tank. I keep that closed unless I'm using the air.
I have a bunch of commercial leak detect stuff at work, think it's
called 'snoop' - I'll bring a bottle home and give it a try.

With the ball valve coming straight off of the tank, I think I've
pretty much ruled out any of my connections, except of course the one
from the tank into the valve. I've used teflon pipe dope on the
connections and cranked them down really tight, so they should be
solid.