Some pictures of what a worn belt might look like.
It had not snapped.. yet.
The other belt I had that DID snap has the same cracks on the outside.
If a moderator wants to move this to Tech, go for it.
The inside of the belt did not show any cracks.
And, for the curious, I use the "9mm socket wrapped in a rag and stuffed between belt and drive pulley with impact wrench" method to remove the nut.