Rebrushing by hand will not yield results same as the original.
As you're a PAM consultant on the forum, you have infinite more experience than I. Have you attempted a rebrush before?
If the satin finishing techniques we use to touch up bracelets won't work on the case , are you suggesting it needs to be sand blasted or machine brushed? In that case he could take the case to a machine shop and have them restore the satin finish?