If you can locate a good aircraft parts and supply place go in and ask them for PRC 1435 or maybe just order some from this link.
PR-1435 Quick Repair Fuel Tank Sealant
PR-1435 is a quick repair, aircraft integral fuel tank sealant. It has a service temperature range from -75?F (-59?C) to 250?F (121?C), with intermittent excursions up to 275?F (135?C). This material is designed for sealing of fuel tanks and other aircraft fuselage sealing applications. The cured sealant maintains elastomeric properties after exposure to both jet fuel and aviation gas.
PR-1435 is a two part, dichromate cured polysulfide compound. The uncured material is suitable for application by extrusion gun or brush. It has excellent adhesion to common aircraft substrates when correctly primed with PR-148 Adhesion Promoter.
Technical Data Sheet for PR-1435