I have a 6.9 IDI that has developed a leak on the outside edge of the valve cover. The gasket is rubber. Should this gasket be put on dry on clean surfaces, or is it better to add some "form a gasket" to help seal the lid? I installed this gasket over a year ago and I used grey form a gasket to help make a solid seal. The other side was done the same way and is still dry. What is the best technique?