The seller may or may not have purposely tried to hide this from you. It may have simply been an oversight and a non-accusatory discussion could still take place. I have found that a by approaching a seller in a calm and non-accusatory fashion (or their Realtor), problems can usually be taken care of in a way satisfactory to both sides. If the seller refuses to do anything, and this was not discovered during the inspection period, you may have no recourse. Perhaps your Realtor could suggest someone who could repair this for you and a reasonable cost.