thinking about all that has been said. This is informative only. Starter armatures run a tight clearance. This is true for many motors. If the armature expands it will drag on the field coils. It sounds like this is what happened to this starter. Also some starters are self supporting while others need a bushing in the bell housing to support the nose end of the starter. If this starter is one of those, a worn bushing can cause the armature to drag on the field coils. I don't know if this is one of those or not.