The image shows one of the brush housings and the old brush remnants (spring and flexible contact). There is a copper coloured inner liner, which can be removed by pressing the metal tab (blue arrow) through the hole in the black plastic brush casing (yellow arrow).

With the liner removed, the cable to the brush can be removed through a hole on the other side (not shown).

In my case, the carbon (graphite) brush had broken up and was mostly missing, so that it was not possible to see what type of brush it was. (Also the spring was free to rattle around and may have caused the slight damage to one of the commutator contacts)