The top cover gasket on the engine is made of rubber. Nice for re-use, but my experience is that it is hard to get it leak-proof when re-installing. The rubber string is tubular and needs some pressure to flatten out. In addition there are two gaps between the sections making up the gasket, where it seems oil could leak.
When adjusting the valves, I decided to try to make a more leak-proof solution. So I just used a piece of white paper to make an impression of the gasket in one piece by pressing the cover down on it. Black oil gave a template that I could cut out with scissors. After bying a 2mm gasket sheet it was fairly easy to cut out the gasket using nail scissors around the sharpest bends.
The gaskets were installed leaving the original rubber gaskets in place. It has worked fine.
