I hope someone reads this as it is still on topic.
Looking at the broken pulley, the inner part and outer part are held together by nothing more than rubber. Maybe they were bonded at some point, but it is still rubber on metal. There are four holes on the outer part (the part where the belts ride) and four holes on the inner part (when the bolt goes through to hold it in place). On the inner part, two of the holes are filled with protruding rubber that then goes through two of the four holes on the outer. It would appear besides this possible bonding process, this rubber helps keep it in place - looks very weak to me.
So when I get my new pulley I don't want the same thing to happen. I'm using this pulley tool:
As you can see, the pins in this tool are only about two inches long - they do not extend far enough to hold onto both the inner and outer pulley. I would almost envision needing to make my own tool where it has pins that are long enough to hold both parts of the pulley instead of holding just the inner while you are trying to put 200+ ft/lb of torque on the thing.
Or am I looking at this wrong and my pulley/rubber bonding just got weak over time?