A bit of platinum rouge on a soft bristle brush in your flex shaft
will do the job nicely. Especially the gesswein 8000 platinum rouge,
as it’s got just a little bit of ‘cut’ to it, but other rouge
compounds should work too, if for the harder metals. If the scratch
is deeper than that, try a bit of white diamond tripoli first, then
the rouge. pearl polishes out pretty easily.