Good story, and excellent pictures! However- - - -you've gone to a lot more effort than necessary. The bushing is made of a sintered bronze material called "oilite", and it's totally unnecessary to cut a slot in the bushing. The oil penetrates right through the bushing. Cutting the slot will cause the oil from the lubricator to flood the bushing and contaminate the brush area with oil, resulting in rapid brush failure and/or intermittent charging due to oil contamination of the commutator.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!