I used the exspensive Nissan sealant. It's supposed to expand as it sets up. It was time consuming to remove the old sealant from the valve covers. I used a razor blade and some high grit sand paper that wouldn't cut the cover, but would remove any residue. I also used a jeweler's screw drive to clean out the groove. I also cleaned the surface with brake cleaner. You need something that evaporates, not oil based. Make sure you tighten the covers in a center-out, criss cross pattern.
