I agree with the statement above...there is nothing that is leak proof...even RDA's with the airflow bored out to the topcap can leak if their o-rings fail or they're simply tilted on their side...nothing is leak proof...that's like saying "your coil never wears out." Well, kinda doesn't...but over a time a coil will degrade to the point that no matter how often you change out your cotton and dry burn and clean the thing it will just oxidize and degrade to the point that it just tastes horrible no matter what and you have to change it out and build a new one...
Same thing with "leak proof" tanks....even if the thing seals up nice and tight...anything with a cotton or any other kind of wicking material will degrade or over saturate over time and wear and tear and fail to hold as much liquid as it could when it is new and will flood the coil, leak into the airflow chamber, or run up the center post....just like if a coil isn't seated properly or not tightened down completely liquid can seep underneath the coil again leaking into the airflow chamber.
Where is the liquid leaking from/to? if you can find the leak you can solve it