Powerhead Gasket Set | Sierra 18-4305 Powerhead Gasket Set Powerhead Gasket Set Contains 18-0851 Relief port twin gasket, 18-0850 Fuel pump mounting gasket, 18-0941 Water jacket cover gasket, 18-0118 Carburetor gasket, 18-0120 Exhaust cover gasket, 18-0128 Powerhead mounting twin gasket, 18-3802 Head gasket, 18-0136 Powerhead mounting gasket, 18-0157 Airbox split twin gasket, 18-0154 Airbox split twin gasket, 18-0159 Airbox split twin gasket, 18-0983 Carburetor to air box twin gasket, 18-0182 Thermostat gasket, 18-0963 Intake manifold twin gasket replaces Mercury 802110 Replaces OMC/Johnson/Evinrude 439083 Replaces Mallory 9-64113