A couple of other ideas for you.
Enamel reducer or white gas [Coleman camp fuel] are usually safe for leather and vinyl. I use them in the upholstery shop when necessary to remove glue. Also, the soft part of velcro works really well. Not the scratchy hook part, but the softer loop part is really good to get into the recesses of materials. Be careful of using cleaners like 409. Sometimes they can be too strong and affect color.
Tricks you learn making custom aircraft interiors.
Loren