i assume your car is a sedan which has the plugs in the center of the valve cover? (98 wagons were the old style engine and body). if oil is in the spark plug wells making the wire ends oily then you do need valve cover gaskets. a gasket set comes with a 3 holed gasket that seals the center of the cover in the plug area. be sure to clean the surfaces the gasket touches and use a some sealer in the sharp corners of the gasket for added sealing. i use brake parts cleaner, compressed air and a rag to clean out the spark plug wells. clean and inspect the plug wires too.