Got a replacement, and maybe I was wrong. The replacement was very different (which is odd since it was the same item, from the same vendor), and came with a Delrin nut instead of a brass nut. I first tried swapping out the lead screw – even worse backlash right from the get go. Then I tried swapping out the brass nut for the Delrin nut, and the backlash disappeared (for both lead screws). The weird part is – if it was the brass nut the whole time – why would I have areas of height where it had sizable backlash then other areas where it had no backlash at all? I wonder how fast Delrin wears out. On the plus side – if I understand Delrin right – you can just put the lead screw back in, heat the lead screw up to Delrin’s melting temperature (since it’s just plastic – Gizmodorks even makes a Delrin/POM/Acetal filament) and it thread forms around your lead screw eliminating backlash again. Question is how fast does it wear – and how often would you need to do that.