You said you made the offer contingent upon the seller fixing the problem; so the issue is not non-disclosure, it is simply breach of contract, IF the contract stated that the “fix the leak” clause surivived closing.
It sounds like you need to present the specific facts and the contract to a local atty. By the way, I don’t really see any liability for the realtor if you knew of the problem, regardless of the fac that is was not on the disclosure form, unless the leak was due to another problem they knew about and didn’t disclose.
We just purchased our house 1 month ago. During the inspection process, we noticed that there was a very slight leak in the basement floor. The previous owners did not disclose this on their disclosure form. As part of our offer, we made it contingent upon them fixing the problem,they agreed and called in a plumber who said that the drain tile was clogged and cleaned it out. That seemed to clear up the problem. Now that we have moved in and signed all the paperwork, the leak is now showing up again. Do we have any recourse against the previous owners or their realtor for this or are we on the hook?