All F-engine Lawnboy 2-cycle mowers with the gas tank integrated in the shroud have a fuel shut off. Depending on year model, some have a long plastic lever, some a stubby lever, but they are the same otherwise. They have a rubber-like gasket between the lever and the tank, that forms a fluid-tight seal, the gas actually flows thru a channel in the plastic lever when "on" between an inlet hole and outlet hole in the gasket. These over time loose their elasticity and start to drip, some in the "on" position, some in the "off" position. Doesn't seem that there are replacement gaskets. Any ideas on repair solution?