The presser foot is removed and so are the feed dogs and bobbin case. It doesn't change anything.
I'm beginning to question if it's something in the bobbin area. I've cleaned it and oiled it and it did not make a difference. I wonder if it might be the stuff under the bobbin area.
While waiting on inspiration and information, I've begun to work on the 750 Leon sent me. The camstack is not cracked.
Also, someone believed in greasing plastic gears, that's for sure. Whether you think you should grease plastic gears or not, these gears are still there. The one under the bobbin area has one tooth missing.
It inspires me to be more generous with my grease.
bkay