I ran into a similar issue with mine as well. However mine is that it tapers closer to the z rails the further down it goes. However when you rotate the couple and lead screw it turns true. I tried fitting it multiple times in different manners with the same result. I dont think it is going to effect much on mine since it does turn true. It will just put a constant pressure on the brass piece. It still turns easy enough by hand so not worried at this point. Will see if it works out. The bearing pocket in mine was loose and doesnt hold the bearing in. But when you sandwhich everything together there is no play.