Yeah, that valve cover. Glue to the cover. Vaseline on the side that goes to the head. It helps keep the gasket located on the cover. And it helps release the cork from the head. If you take the valve cover off a few times it should still seal. If you are using a 216 valve cover it helps keep the gasket under the cover on the manifold side. The valve cover needs to be gently flattened to match the head. If you don't it will leak. I have used the weather strip cement, it works well but can be messy. I like the black 3 M stuff. Motor oil works if you have some open. The brand and "weight" don't matter. I do prefer to glue the pan gasket to the block. You can see when all the holes line up and it stays in place. The weatherstrip cement works well at the joint were the rubber seal meets the pan gasket. At the front and the back. I have had the best seal with the cork in place first. Then the rubber strip. Then cement in the junction.It will stay soft for a bit while you place the pan and start the cap screws. It will seal those corners rather nicely. A wire wheel cleans off the gasket junk on the cover.

Steve H