Toilet leaks even with water shut off

I have a toilet from hell!

I'm installing a new toilet in a room where the flange is nearly flush with the floor, but even after using 2-3 different wax rings, all of which are extra large (I even tried stacking them), my toilet still leaks from the bottom onto the floor.

The really odd thing about this leak, is that it occurs even after my water is shut off (a slow leak that you only notice after hours / days). This seems to indicate that the leak is not with the wax ring seal, since it leaks even when there is no water running to that part of the toilet.

Is my toilet cracked? I'm not sure what to do and I'd hate to install yet another wax ring only to have the thing leak yet again.

Help!

Check the gasket between the tank and bowl. It can also be from the flush valve gasket. Check the nut that holds the flush valve to the tank many times they not tightened enough from the manufacture.

Defective Toilet. Rare but happens occasionally.

Here's how to check.
Remove toilet.
Take it outside and set it on some blocks of wood.

Pour some water into the bowl

Get a mirror and check the cavity under the bottom.