I'm not very experienced with rebuildables, but I have a Fogger v4.1 and have stopped my leaking problems. If it's leaking out of the air-holes, IME, you need more wick in the juice channels. I don't fill them up or anything, but I do make sure there is at least some wick in the top of the channels to keep too much juice from getting in the chimney where it can run out through the air holes.
If it's leaking out around the rim of the tank it's probably the o-rings, they're very temperamental. If you tighten too much (or with dry rings) it can push the bottom O-ring up and make it bow, causing juice to leak out during filling. It can be hard to see this, you have to take the tank apart and you'll notice the bottom O-ring is popped up somewhat.
You may have a different problem these are just two issues I encountered and resolved.