Its actually the airflow screws. They back out way too easily. The air flow screws get stuck in the milled "nuclear" symbol that is in the top cap of the panzer. Other mods have the milled airflow channels that the screws get stuck in. I know its not the contact pin because I took it all the way out of the panzer and it was still stuck. I'm thinking a piece of tape or even a pre-cut sticker that you could stick to the bottom would fix it. I can make them as well. Just when you need to fill it, either use the top fill method or poke a hole where the juice fill screw is.
For a while I hated my kayfun but when it finally came unstuck I started loving it. Every time I used the top fill method it would leak. I'm so happy I can fill it from the bottom. Fresh build, fill it up, no leaking, dropped it on my duquit box mod, looks sick, couldn't be happier.