It may not be the foot at all that's causing you problems. Someone else posted here that she started suddenly having trouble sewing and it turned out to be the fabric; one fabric in particular just was not playing nice. Are you sewing on EXACTLY the same fabrics as when it was working? Not just same manufacturer, but same color and everything? There might be something else you can adjust to make it work properly.
Have you tried changing the needle itself? Maybe it got a little bent at some point and that's why you're having trouble with layers? Can you stitch through the quilt without the walking foot on OK?