What is an easy method of proving that a cryptographic oracle attack is possible? Lets say an application is using CBC mode without authentication.  The application is generating cipher text.  This cipher text can be manipulated by the attacker and then transmitted back to the application. 

Without looking at the code, what is an easy method for the attacker to prove that a Padding Oracle or Decryption Oracle is present?  Is there a method more elegant than brute force manipulation of the cipher text?
We have a Padding Oracle if there is a different response from the server gives us an indication of the correctness of the pad (say if this needs proving). We can establish this by playing a game where we send badly padded cipher-text and random strings to the server, finally submitting some at random and seeing if we can get a non-negligible Advantage is guessing which one we sent. 

The problem is that this might be the "brute force" way. It's fairly easy to do if there is obvious data-leakage, but you have to check through a lot of side-channel attacks to rule out data-leakage to an efficient adversary. I sense you want a clever fast way to prove there is no data-leakage, which doesn't sound possible to me.