An update: I upgraded the 4th articulation bearing. I just printed a few differently scaled versions as mentioned, picked the smoothest one and added tons of lithium grease between the balls. It now works like a charm. I also did paint the optic disk with some different paint and now it homes perfectly. I don’t know if it was because of the earlier bearing (it was wiggly) or the paint, but finally I am a proud owner of a fully functioning Thor. ^_^