Had the same arms on for 2 months. Apparently that is too long. Haha.
LOoks like the tensioner or belt might have got at it. One time I ran the belt too loose for a few laps before I remembered to tighten. Pully is still totally useable.
Working on the diffs now... Changing front to 30k from 20k. Then the rear to 5k from 7k.
Tight technical indoor track.