When you buy a pre-owned house, the general rule is caveat emptor (buyer beware), which means that you take the property as you find it, unless agreed otherwise, subject to the duty to disclose known latent defects.
The general duty at common law was to disclose known latent defects not discoverable through physical inspection of the property. The disclosure form adds specificity and broadens this obligation somewhat, but not in a way that is really material to this case. Most importantly, neither the common law, nor the standard real estate disclosures form in California, requires disclosure of defects that the seller believes sincerely and good faith, were resolved prior to sale.
If the seller sincerely and to the best of his knowledge (and the knowledge of his realtor) believed that the repairs he did had fully solved any leakage problems with the house, then there would be no duty to disclose them.
But, if the seller actually was aware of past leakage problems but knew that they weren't resolved or didn't have any genuine knowledge regarding whether the past problems had been resolved or not, there is probably no liability.
Also, you probably can't successfully sue the inspector for any meaningful amount of money for failing to discovery the problem, because home inspects routinely contractually limit damages for their defective work to a return of up to 100% of the fee which is almost surely trivial relative to the cost of fixing the problem.
So, your entitlement to relief would depend upon the knowledge of the seller and the seller's agents, and you could do research to see if it is plausible that the seller knew that this was still a problem.
On the other hand, even if you couldn't get the seller to actually pay to fix things, the seller might be convinced to transfer and assign any rights the seller had against the people who did defective repair work to you, if the real estate contract didn't already do so. The seller could have sued them for negligent work, or for breach of a warranty, if any, of their work. You may have the right to sue the contractors who did the defective repair work for negligence anyway, but it would be easier with the seller's cooperation.
Depending upon the costs of repair, pursuing the contractors who did the repair work legally or simply by legal demands, might be more cost effective than pursuing the seller, since the litigation costs of proving what the seller knew or didn't know might be very high relative to the amount in controversy, and depending upon the terms of the real estate contract, you may not necessarily have a right to attorney fees if you prevail against the seller. You wouldn't in a common law fraudulent concealment lawsuit, and the contract may or may not modify the common law rule.
Realistically, it is very hard to make a lawsuit like this cost effective unless the cost of repairs is in the many tens of thousands of dollars or more. It isn't clear how much it will take to fix the problem and your first step would be to hire someone to diagnose the problem and give you an estimate. A diagnosis of the problem by a construction professional, and a review of the permits for repairs done prior to sale, should also help you evaluate how hard or easy it will be to prove that the seller was aware of the latent defect, if indeed, the seller was aware of it.
