I purchased a 9" angle grinder (Wolf) on eBay. After using it for about 30
minutes, one of the brushes started sparking badly. I could hear the arcimh
amd and see the flashes right through the yellow casing! I removed the
inspection cover and ran the grinder, I could see bright blue sparking
travelling right around the commutator ()if that's the segmented copper
drum that the brushes rub against) and flying out from where the nearest
brush contacts the commutator. Is this something I should worry about, or
is it normal? Is there any maintenance operation I can do to cure it?

Thank you.

Al