Loctite 518 Flange Sealant for Fuel Pump O-Ring 50mL.
This is the Aprilia/Piaggio/Moto Guzzi recommended compound to put on the fuel pump flange O-ring/Gasket anytime you have to remove your fuel pump from the models listed in the complete fitment list at bottom of this page.
Please note that this sealant can not take up gaps greater than 0.50mm. If you apply this sealant and the fuel tank leaks, you probably have a warped fuel tank.