One of my tanks was leaking, but it stopped when I pulled off the punched-out circle of plastic that was hanging from the inside of the lid when I took it off. (the "hanging chad".)
Absolutely get rid of the "hanging CHAD"!!! Displacement and leaking will occur if the "chad" is bobbing around. It can rub along the wick and break the vacuum seal that the liquid creates with the wick housing.