The last 228 I had (a 1951 model) used a rubber grommet which was a stepped affair (larger on the part which sat on top of the valve cover and the smaller stepped part fit snugly right inside the valve cover hole and was a fairly tight fit on the mounting stud), then on top of that was a flat washer the same size as the diameter of the grommet and holding it all in place was an acorn nut which if you had a new gasket and new grommets would only catch about 3 or 4 threads of the mounting stud before it started getting tight. And you didn't want to tighten it too much or you would mess it up. There was no tapered nut anywhere on mine, but maybe something changed between 1949 and 1951. That is my guess. Parts stores sold those grommets and when you bought them, they often also included new washers in the box. The acorn nut and that washer pushed the grommet down tight on the valve cover and in turn pushed the valve cover down on the head. Then there was one gasket about 5/16 inch thick glued to the valve cover and as already mentioned the surface of the valve cover needed to be very flat and at right angles to the vertical part of the valve cover...that was important. If it wasn't all straight and right, it would leak cheerfully. If you glued 2 gaskets to the valve cover, you never would have been able to start the acorn nut. Even if you did everything correctly, it was likely to leak after a few weeks.
