I believe your problem with leaking is my same problem (after a cleaning), that is, not enough vegetable glue sealing off the stem pieces opposite the slits where the wicks protrude. I have a double jeweler's monocle that I can attach to my glasses. Lets me look REALLY close at something. I can clearly see that parts of the stem has glue and parts don't. Looks like the glue was "daubed" in place and not smeared around to cover the whole surface area of the stem. Because of this, juice seeps in between the stem and the metal base of the connector, floods the bottom of the cup under the coil, and right out the air hole in the bottom of the connector.
Now to qualify my answer, I didn't suffer any leaks until after I took this carto completely apart to see how it worked and clean the coil, and then took it apart again to discover the source of my now present leak (I had hoped it worked as well as the clearomizers seem to as far as them not leaking subsequent to dis-assembly and re-assembly as I haven't had a leak yet on that carto). I believe that even though there were areas of the stem not glued and sealed in place initially, the fact that my juice is thick kept it from seeping past those voids of missing glue. It should be noted that I could see a noticeable gap (under magnification) between the stem and the connector wall. Without glue to seal off this gap, gravity is going to force the juice up into the voids and over the top of the connector, down into the cup.
"Enough" of a seal was created (for me) by the daubing the glue in place. I think that as a QC and process improvement idea I would have the factory change their process so the glue is smeared or painted on the inside of the stem as opposed to it being daubed in place. It may very well be that it was intended that during the manufacturing process the glue was supposed to be more evenly spread out, perhaps by the action of assembling the pieces together. Regardless, this would be the first thing I'd get changed as I think that will resolve the leaking right out of the box issues some are having.