Do I have any recourse when the seller of a used 5th wheel hid substantial water damage to the vehicle?

In Northern California, I bought a used 5th wheel, and the seller told me it needed deferred maintenance, and that it had an old leak from a missing fan cover. He said he had stopped the leak, and it hadn't leaked during the time he owned it (several years). After I brought it home, I found one place where the original leak damage occurred was not only wet and soft, I could actually put my finger through the wall.

When I spoke to the seller, he maintained he had accurately described the vehicle, and I feel, by telling me the leak was from years ago, and had not recurred, he did not accurately inform me of this specific problem. I believe he should help pay for the repair of the wet wall and he disagrees. Do I have any recourse in this situation?