I would use the RetroClean on it. However, if it's an unquilted top, I would either quilt it first or baste the top to a backing fabric before soaking. If you are not careful with a quilt top, you can end up with a tangled mess of seams on the back, unexpected shrinkage and distortion, etc. When fabrics are quilted closely to a batting, the batting controls shrinkage. When fabrics are washed alone, they shrink at whatever their individual rates are. Plus, seams can fray.