I see that you have tried everything. I have a couple of small Brothers too and sometimes I don't realize that the bobbin thread jumps out of that little hook thing in the bobbin case and it causes very wonky stitches. I always think I have done it correctly and maybe I have but it jumps out. Maybe if you haven't checked that it is a possibility? The Brothers are usually trouble free so I hope your problem is easily fixed. Keep us posted.