I didn't even use WD-40 because the internet said it wasn't necessarily the best stuff for removing a rusted nut. I went straight for this stuff instead, which is supposed to be much better for loosening stuck threads. It was pretty amazing stuff because the existing rust on the thread simply vanished when I sprayed it on there. But the nut was still just too stuck. I was using a basin wrench, the blaster stuff, and all sorts of other things and it wasn't budging. Ah well, live and learn.