[chevy_mike]

With a PCV connected, you need some source of fresh, filtered air to come into the engine, otherwise you create a vacuum inside, which can pull seals in and then create a leak. Stock setups typically had a port that connected to the underside of the air cleaner. That is ideal as you typically won't get any oil to splash up into that area. With a breather right on the valve cover, if there is no splash shield inside the valve cover, oil will be flung into the breather, which will eventually cause oil on the outside of the valve cover.