I would suggest that the screw hole on your 1/4" foot has slightly enlarged with age, maybe hardly enough to barely even measure. Or the threads on your screw are slightly worn down. You could put a piece of electrical tape on one small part of the hole, then attach to the machine and see if that tightens the screw up enough to hold the foot securely. The cost of a new screw and foot isi probably cheaper than having a tap and die job done to redrill the foot and use a larger screw - plus it would foul up all of your other feet on that machine.
After I've said all of this, I would recommend going to Ebay and buying a new foot and a new screw. You will probably find it cheaper there than at the dealers.