the screw on my walking foot keeps coming loose as well, I'm just trained myself to tighten it every hour or so. If it was loose and shifted, it could have bent/broken your needle and that jarring might have bent the walking foot as well.
sounds like you've tried out everything, and not sure what the issue is. If you purchased it at your brother dealer, it should be compatible with your machine, but you might want to take the machine in and let them see what happened - they might have some other ideas. but that might have to wait till after the Christmas rush, huh?