The cork gaskets come from the manufacturer bone dry. Oil absorption is required or them to seal properly. I glue mine to the valve cover while they are still dry, then apply enough oil, just shy of sloppy wet, and button everything up. As the cork absorbs the oil which is wiped on it, in addition to engine oil splashing around under the valve cover, it swells and improves the sealing action. That is why it is not necessary to really crank down the screws.
