Like is said, nothing really ever good comes from a secret. Pride and Humility have no place together. When Spiritual Principles are in conflict with defects of character, somethings wrong, because Spiritual Principles are NEVER in conflict.
He is doing alot to tear you down, and yes you might expose something about him you think he may not make it out clean, but what about you, isn't your recovery worth getting over this. I don't really think there is anything to prove here, just that you want all the B*llsh!t to end, and to move on.
Actually he is hurting his sponsee's and you are watching it all from the side lines, we don't have to act on hurt by hurting others, but we do need to move on. Even if you write a letter with out sending it, talking about it at meetings, go to some outside meetings that he won't be at, You don't ever have to use again and you know that. You don't have to live like this either. Cockiness is a redlight indicator!! What doesn't come out in the wash, comes out in the rinse.
Peace,
Todd J.