Well, it's been a year since I fixed up this machine and guess what? I finally found the lost presser foot! It was wedged right between the seat cushion and arm of my rocking chair - I was sitting on it today and just happened to look down, and there it was. I can't believe I didn't find it during my initial search; I felt down the sides and back of a couch and chair on the other side of the room, but never looked here.