Probably was a user error fitting the coil but it was a while back. I seem to remember liquid seeping out of the air holes and also some gurgling.
The ohm brew I have at the moment is Nic Salts but before it was just the normal stuff.
could be a duff zenith with a moody seal on lid allowing air in & upset the setup
coil drops in with lugs that align, it is a bit snug so careful alignment required
but air ring will have a gap in between tank & afc ring if coil not located correctly
any leak will allow the juice to begin to flow & flow leading to flooding & leaks
you might have duff zenith with moody lid seal ???
sometimes the zenith coil can have a very faint gurgle as they get old or if juice is a bit runny
flick or gently blow through the tank (modestly not blast it) will ensure the odd droplet disappears
doesn't happen that often, just on some juices or coils if they are getting on a bit
but really very faint gurgling - nothing like some real lemons I have had sounding like the dregs of a milkshake
you got a couple of decent tanks/setups - think it is pointing to juice but you tried other stuff you have said
either you just have bad luck with moody tanks/coils/juice or you are just jinxed
I'd try some decent juice highly recommended - so what's ya poison/flavour of juice ???
hopefully once you give a clue then others can chime with...
Try this or that - it is the nutz & works a dream with the XR-2300 & XR-2200 (airplane)
well that sort of crap is my hunch