"Don Foreman" moaned
Both brushes just seem to have seized solid in the brass channels. I
can't
pull them out using the copper cable, because I sense that if I pull
much harder it will break away from the carbon block.

Some sintered copper/graphite brushes will swell upon long exposure to
moisture. You may have to distort the brush guides to get them out....
essentially, they're corrosion-welded to the guides.

LLoyd