[Keith True]

The shaft is part of the armature.Over the years that shaft might have been bent,rebent,pounded with a hammer,something might have gotten between the gears and bent it,could be one of a dozen reasons for it to break.The starter may have stayed engaged while someone ran the engine any time in the last 85 years.If it was mine I would replace the armature,redo the field coils to 12 volt,and use it.I really don't like the way they slam into the flywheel when engaged using the 6 volt setup.I never heard of an aluminum housing on a A or B starter either.That's new to me.