I have soaked a number of "vintage" fabrics in powdered oxyclean dissolved in water, and they all came out beautiful. The old yellowed pillowcase is not yellow anymore, and I soaked the GFG unfinished top in it, too. After I fixed all the problems on it, the rust stains, the chewed up side, the pieces that had frayed apart. I noticed that it had some kind of weird pleasantly scented stains on it. I learned the hard way that we do not wash tops before they are sandwiched, but I also didn't want to do all that stitching on the quilting, and then not like the fact that it had stains. It's an old top, and is quite faded, not sure why, but it's made from old fabrics that I like, so I'm going to use it on our bed. (tried it the other night because it was really cold, and it was great! Still not quilted though, lol.)
Anyway, I sewed the layers together and birthed it, sewed the hole shut, sewed all the way around the edge, and soaked it for 2 or 3 days. (I use a lot of disappearing glue stick, and when I first put it in, the water turned purple, which freaked me out a little, til I figured out what it was.) I did it in a plastic tub in my bath tub. Dumped it out, gently pressed it to get out the soak solution, and then filled the tub up a few inches to rinse it. Dainty, dainty, tender , blah, blah. Did that a couple of times, then put it in my front loader to spin. Laid it out in my sewing room with a fan on it instead of drying it in the dryer. All the ick was gone, and its in great shape. So, I say, try that. It worked for me.