I have collected vintage quilts for years. I use Retro Clean to get stains & yellowing out when needed. I fill the washer with cold water, then add the quilt & make sure it's completely soaked before adding the Retro Clean. Let it soak for a good hour, then begin the gentle cycle setting. Sometimes it takes more than one wash, but I have never had a quilt 'fall apart' using this method.
Use caution when removing the heavy, wet quilt out of the washer. I put mine in the dryer on the lowest heat setting.
Good luck!