somewhere in my collection of info is a tech article on brushes
many of the commercial brushes are laminated with low resistance layer on the inside
and higher resistance material on the outside, this cuts down arcing and greatly increases brush and commutator life.
i have no idea whether these smaller motors use the same technology or not
i suspect not.
recently i picked up an assortment of large brushes, some about 1/2 x 2 inch and about 3 inches long, some had been sitting in water and started to delaminate
(of course i picked brushes still in sealed bags out of the crate) but looking at those that were seperating clearly illustrated what the book talked about.
btw, i got the brushes for something like 2 bucks a pound, and got several sets
thinking they might be useful someday for a down the tower slip ring setup.
all have very large braided copper leads so they look like they might be easy to work with.
bob g