It's not the lint under the case causing the trouble (although that might help somewhat). It's the oil wick that dries out in that little hole under the bobbin case. It makes a huge difference!!! It doesn't seem to dry out on every Janome, just some of them. One drop of oil in that place will probably fix your problems. Since I now keep that spot oiled in addition to the places mentioned in the manual, I have had no more trouble.