I have never heard nor seen anything like that. For 6 plus years now I have not had a leak in my valve covers. I used what came in the fel pro gasket kit. I used permatex ultra pluss rtv on both sides of the gasket. That way there is no chance of a leak. Also make sure the torque spreaders are flat and the valve cover gasket surface is flat too. Sometimes the bolts are tightened down so tight they crush the gaskets and dent the pan rail creating a bigger leak. Once a leak starts its nearly impossible to tighten it to fix it. The oil has made a path and it will wick out no matter what you do. When a gasket cracks and you tighten it that usually makes the leak worse. This is the main reason we never use a cork or rubber oil pan gasket. They shrink, crack and leak. Then it tuff to fix.
