There is no guarantee that the seller had knowledge or had this happen to them. We have had some serious rain this spring, and it is possible this is what it took to flood the basement. The thing you need to make sure of is that the downspouts are clear, of sufficient size to accommodate a heavy rain, and that they move sufficiently away from the house. The grade around the foundation needs to move away from the house. If you have drain tile, you need to have a sump pump with a battery back up. If you have a pump, test it to make sure it works. Should you have all of these things, you are unlikely to have a water problem. Spend your money fixing the issue. It could cost you a fortune going the legal route and you may not win. Good luck to you!