Sorry it's just my terminology, it's called emery if it has grit on it. Most likely it was al-ox paper which is probably wrong as well but it is still working after two years of use so I'm not going to take it to bits to do it with the right stuffIt might be worth asking if it can be repaired as I did it with a circular saw ages ago and it was repaired for £35 with a years warranty on the repair.
Only using sandpaper, not emery (which is a form of al-ox) is what I've read in a few maintenance instructions and I imagined was because sand is softer and stray particles are less likely to do damage. If there are proper products for the job, it makes sense to use them if you can and if it's a job you have to do anything like regularly. Something you absolutely shouldn't use is steel wool for the obvious reason that you can get conductive particles.
The last time I had a problem with a commutator was a year back with an SDS drill that suddenly began to start only when it was jolted. It was enough to clean the commutator segments with IPA on a cotton bud, without removing the brushes and without using any abrasive.
