I have a Bernina 530-1 Record (an old treasure), and was cleaning and oiling the bobbin/shuttle area. I also removed the round plate behind the shuttle (it's round with a screw hole in the center). I reassembled everything in what seems to be the only possible way, but my bobbin case won't seat properly. When I turn the hand wheel, the bobbin case pops out. What am I doing wrong? I've posted this question on the ThirtySomething group, but thought I would also try here. Thanks in advance for any suggestions.