The balancer came off pretty easily. I didn't need to use a puller. There was a lot of front to rear movement and I just gave it a nudge with a socket extension to get it the rest of the way off.
As for a reason for the failure, I'm thinking the big bolt wasn't tightened to proper torque or the cup spring flattened out and the bolt loosened up. The cup springs look more like flat washers.
I've got some pics but I need to resize them to post them.