How do you replace a valve cover gasket in a 1998 Toyota Camry?

Remove the spark plug wires from the spark plugs, then remove the large nuts (30mm) around them that hold the valve cover down. If the valve cover is stuck, knock it loose, gently, with a rubber mallet or wood block.

Remove the old gasket and spark plug tube seals from the valve cover. Clean all mating surfaces, including the top edge of the cylinder head, and place the new gaskets/seals where the old ones were.

Place the valve cover back on the head, tighten the nuts down on the spark plug tubes, and place the plug wire ends on the same spark plugs they came from.