if the leak is coming from the back of the motor i would suggest crawling under it and looking if the rear main is leaking that is a huge flaw that ford had in that body style and the one before it i have a 91 ford and it leaked oil from the rear main, other then that putting in valve cover gaskets is pretty straight forward, just watch out those trucks are vacuum line hell, the fuel rails should be connected on the inside of each valve cover using the same bolts you will have to pull them up and work around them, make sure you use, paper towels when you are cleaning up the gasket to keep as much out as possible and use a "shop vac" and vacuum out the area including around the rocker arms and after you finish, change the oil as for what gaskets to use i normally run "NAPA" gaskets and they work great have yet to have a problem with them.
