Yep, happened to me too. First off, you can't let it get that low; I'm surprised it's not gurgling at you, or making the
juice taste bad, burned. You should never let it get below at least 1ml, actually about 1.6, mine starts gurgling and sometimes gives a nasty taste from burnt
juice -- the coil is right there at the bottom and needs a sufficient amount of
juice on it, or it will burn what little is left.
You need to take the base off, as you do when you refill it, and have a look at the two little rubber o-rings, or gaskets, on the base itself, not on the coil. The smaller one, near where the coil screws in, should lay perfectly flat on the ridge where it sits. Mine was not, and it was practically drowning my battery. If you can't get that flat ring to lay perfectly flat, you should get a new base; they're cheap. Or maybe you could just replace that flat rubber ring. I got a new base, and now it doesn't leak.
Hope that helps,
Andria