You need a complete valve cover gasket SET and install all componets in this set, it comes with the tube seals and other gromets. The old seals is where the oil is getting into the plug wells. 'Very' RARE for tubes to leak at the bottom but it can happen. Tubes are threaded into cyl head, and have to be removed to reseal. With a pair of these new super grip slip joint plires you can grip the tube in the center and turn it out, a good spraying of carb. cleaner around the tube at the bottom will help. NOW, IF IN DOUBT SEEK A MECHANIC!!!