I have a 31-20 that Steve gifted me in the garage, but I don't think I can be of much help to any of the questions. I think the hook/bobbin assembly is different on my machine and I've not even spent more than 10 mins with it. Life has sort of gotten in the way and I've had a full plate the last few months. But, if need be I can try to see if it has the same issues or at least take a few pics to work off of, if it will help.