401 thread snapping

I've been loving sewing on my 401 until all of a sudden, today, it started giving me some weird trouble. It started off with the zigzag stitch, which always has a tendency to skip a stitch or two if I'm not careful, but after a bit of sewing started getting worse and worse until it wouldn't pull the bobbin thread up at all. I tried a bunch of different needles and fiddled with my tension. Absolutely no luck, at which point I tried to go back to just a straight stitch, and now my thread keeps snapping. When it does run, it'll lay down a couple nice stitches, but then seems to run into an issue of Not picking up the Bobbin thread again before the thread snaps. I've tried four different needles, re-threaded the upper attention, repeatedly, clean the machine, took the bobbin out and put it back in over and over, opened up the whole machine and oiled everything, to no avail. My upper tension is back to where it normally is, but I've also tried greater or lesser tension. I haven't messed with the Bobbin tension at all, but it definitely seems like that's the issue: I guess the thread is snapping at the lowest point of the needle motion. Any suggestions?