I just replaced my right side valve cover gasket. You have to take a lot of stuff apart to get to it. Once you get everything out of the way, you still have to carefully maneuver the valve cover to get it out. Getting the fuel injector electrical wire connections disconnected was probably one of the worst things for me because I didn't know how to do it, I didn't have a tool for it and they are buried so deep I could not see what I was doing. You also need a metric, deep socket set for the valve cover bolts. I think they are 7 mm.
It is very difficult to get the valve cover out of there without knocking some dirt on the clean part of the head. I took care to make sure the top of the head and cam was very clean before reassembling. You then have to take care not to knock more dirt in there when refitting the valve cover. It is particularly important to make sure the surface, that the gasket contacts, is free of debris and dirt.
I am going to wait until the left side starts leaking before I take on changing it. After seeing how hard the rubber gasket was on the right side, I know it will not be long before I have to change the left one.
2002 FX4 Bright Red Supercab 4.0 SOHC, manual 5-spd & Tcase, 33" BFG MTs, K&N air filter, Modified air box inlet, Gibson SS cat. back exhaust, Bama flash, Hidden Hitch round receiver, Rear helper air springs, Electric trailer brake controller, Line-X bed liner, WAAG bar with KC lights and Wildernest shell.