Excuse me for bumping this topic, but I would just like to say a big thanks to all of you. Especially Julia. The small M3 bolt fixed the problem I have been struggling with for more than half a year. I replaced and cleaned almost everything on the printer. I was ready to throw it out of the window. Then I read your post, looked at the screw, saw the deformation you described. There is also a circular mark on the extruder motor from the bearing, indicating that it was rubbing. New screw and everything is fixed… Unbelievable.
Nevertheless I think this is a bad design from Zortrax. The bearing on a threaded part doesn’t make sense.