Because some balls are done with huge differences between consecutive grit applications (500 grit FEPA followed by 4000 grit FEPA), and because you are trying to REFRESH the surface, I'd tend to suggest you always use at least the last 2 grit levels during the refresh process, whether you do it by hand or by spinner. However, as an aside, since the surface was probably done by spinner to at the start, UNLESS YOU DID YOUR OWN SURFACE BEFORE EVER USING THE BALL, I'd strongly suggest imitating the original surface process.
So if it was 500 grit + 4000 grit by spinner, do it by spinner.
If it was 1000, 2000 4000 by hand, do 2000 grit, then 4000 grit by hand.
If it was 1000, 2000 4000 by spinner, do 2000 grit, then 4000 grit by spinner.
ALWAYS use water.
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