The post part where the atomizer head screws in and the base part that screws onto the battery are press-fit together. The post can get out of alignment with the rest of the assembly, allowing juice to get past the silicone gasket on top of the head and flood the atomizer.
If you take the top screw cap off and look straight down into the assembly, the post should be right in the center. If it isn't, you'll need to tweak it a bit to fix it.
If the post is centered correctly, the top cap makes a seal with the silicone piece, only allowing juice to come through where the wick is.
First time I noticed that the base and post were two separate pieces is when I dropped it, and it wound up way off center. I carefully tweaked it while still attached to the battery until it was right in the middle again.
I haven't had a silicone cap wear out on me yet, but I keep all the parts when rebuilding or replacing the head just in case.
*edit* best way to see if you're out of alignment is to simply take off the drip tip and look down into the tank. You should see the silicone cap right in the middle of the hole, with no gaps.