Alcan window balance 3606

This balance is stamped "3606," but I do not see that selection from which to order from the S380 series 37" balance. So I weighed the window and it was 34.2#. Therefore, based on the weight range for the S380 series, I am assuming it would be a 3650. Can you verify?

Also I just installed a S380 - 37" 3640 in one of my windows and during installation one of the pulley wheels partially disintegrated from this new balance. The balance works, but I'm not sure if this pulley is compromised and will fail as it is used.

Just spoke with a rep on the phone and she verified that if the stamp does not match up, that weight determines which balance to get. Therefore the 3650 would be the proper item.