What can/can't a player say regarding the cards drawn from and replaced on top of the Destiny Deck using Leoben's special ability?

I doubt they can say "I kept a 4 and 5 of Leadership". But can they list the type of card they drew or placed on top of the deck (ie. "I drew a Treachery or I placed a Engineering"). Or do they have to be really vague about it ("The cards I placed on the deck were better than the ones I drew from it.")

Any advice on this would be helpful. Even if it's just to point me to where I need to look to find this information in the rule book/FAQ.

I'd say that you couldn't say anything until a crisis card comes up... then the secrecy rules(which I believe you can find in the FAQ?) would apply, allowing you to say "I'm helping a lot"... or "I'm helping a little".

Since all you're allowed to say when contributing to Skill Checks is "helping (or hurting) a lot (or a little)", I don't think you should say anything about the cards you draw or put back.

When I played Leoben in a recent game and people asked what it was like, I always just said "You'll see".