You should definitely try to fight this. You shouldn't be held responsible for an issue like this when it wasn't your fault, and the problem existed before you even moved into the house. I know that I would hate to have to handle someone else's problem. You should talk to inspectors and real estate agents at the least. If you feel the need though, you should also talk to a lawyer to see what they can do to help you. That's the best chance you have at getting the help you need.