I have a 93 Ranger with the 4.0L and just recently I had to replace the valve covers due to rust eating a couple of pinholes in the drivers side cover and the passenger side cover was about to do the same. The only place that I could find them was at the dealership for a cool $150.($100 for the right side, $50 for the left side) For valve cover gaskets(about $30 which includes upper and lower intake manifold gaskets), I went with the Fel-Pro Permadry Plus from autozone. No RTV silicone required and they were easy to install. Now 10,000 miles later, no leaks! I also used the same gaskets on my 2.9L I just rebuilt. I've put about 1,000 on it and no leaks.

If your using the same valve covers, make sure the surface that contacts the gasket is straight and flat.