Such a good person , that VagCookie ! <| sep |> cut them out <| sep |> It really depends on what your personal needs are . Do you want to preserve the door as an historic example , or do you want to keep spiders from coming in and biting your kids ? A quality restoration would probably involve disassembling the door and gluing up that panel . Maybe making modifications to the stiles andor round part to allow for seasonal movement if that is an issue . It would be tricky for most people , the method of jointery may not be obvious , you could get involved with the glazing of the lites which could be a can of worms , the finish is delicate , etc . If a quality professional restoration is beyond practical , then I think a low impact modification such as a vertical trim piece on the front and back covering the split . If the panels can be moved in the railsstiles maybe you could come up with a clever way to glue the panel back together in place . It would probably involve some real trickery with clamps .