Slightly related, I have found that the znut holder seems like a weak point in the design. It seriously difficult to swap out and is easy to snap the screws out the side. I have modified it to beef up the margins between the screw hole and the outer edge. A future redesign would be nice. Maybe have the bolts flipped around and held captive within the z-middle. Then to mount the znut, you push it down on to the bolts and thread the nuts. This would allow servicing the znut without tearing the whole machine apart.
Attached are my modification to the znut. Though, I should have slanted the outter edges to not collide with anything.