I've cleaned and buffed all the pieces, took it all apart and examined everything, went over it with 800 grit and oil. The thread comes down around the bobbin with each stitch and is pulled up. Every once in a while, the loop hangs up, the next loop comes down and pulls it all up. (Can you see me practically standing on my head to watch this process while sewing very, very slowly?)
She didn't have a bobbin case and I've bought two, both are not Simanco, but stamped Iris. They both seem to rattle around a bit, maybe are not quite a good fit. I like a mystery but may have to set the 301 up for the third machine, there is sewing I've got to get done. I'll quit venting now.