The new bobbin case should work well. Why isn't it? The needle hole and upper is in exactly the same spot it should be, at the right time. It doesn't interfere with bobbin case or thread formation, and it has been tested by more than one person. I can understand adjusting the needle bar for a 15x1 needle will offset the point where the needle hole passes just enough to interefere, but if you use the new bobbin case it seems to sort out any problems? Neither is there any problem with continued use of 206x13 needles.