I use TiteSeal light in an industrial application in an area that gets over 500 deg. F and it holds up very well. That being said, I would buy stock in anything Mel suggests.
I had to re-do all the brake and fuel line fittings AFTER the airplane had flown 10-15 hours. MATCO recommended 567 and I haven't had a problem since. Believe me, It's a LOT easier to do before you build the rest of the airplane around those fittings.