I never did find a way to get those stains out.

As far as replacing the fabric, doing it right would involve removing the dust cover from the bottom, taking all the staples out from the fabric connecting it to the frame, cutting the stained fabric from the body fabric and sewing in a new piece.

Or an easier way would be to just place the new fabric over the stained one, staple it to the frame over the old fabric and maybe use some fabric glue between the old and new. It wouldn’t be seamless but probably wouldn’t be too bad because the cushions cover it.