I was reading the reviews and several mentioned that you really have to get Grinding Chamber and Base glued in perfectly otherwise it will bind. It looks like the plastic end of the Grinding Chamber that slides in first is smaller than the Base giving it some wiggle room. I wonder if I 3D printed a thin spacer sleeve and slid that in from the top to center the top portion if that would solve the problem? 

I pretty much assemble the whole thing when I install the chamber.  I use 5 minute epoxy so I'll use the plunger and the base to make sure there's no binding and let the epoxy set for a few minutes then remove the base to make sure I don't accidentally glue it in place.  I don't know that a 3DP sleeve would really work because the plunger really needs to be aligned with the base piece moreso than with the grinding chamber.