In California, definitely the seller's. Although as agents we have to sign the disclosure off; so if the agent knows that as a fact and the seller is not disclosing it, the agent should give the seller gentle reminder / advise that it is important to disclose, disclose and disclose everything that is known to have a material effect on the property.
We also ask the clients to order a third party Natural Hazard Disclose and the Clue report. The cost is minimum (around $100 or so) and in our area, the sellers will customarily pay for the cost of getting the report.
I saw the box Ed.
In FL, it is a seller's responsibility to disclose any visible or non-visible defects/issues which may affect the value of a property. It is then the listing agent's responsibility to relay this information to any potential buyers or buyer's agents. Real estate law varies from state to state, but I do believe this is a standard practice in the industry. This is just one example of why having a REALTOR represent your interest as a buyer's agent, is so essential. Best of luck!