I pulled the fuel tank to clean and seal the inside with POR 15. I noticed that the top has a small hair line crack about 1" long. Has anyone used POR 15 to seal these cracks, or should I have a patch applied? Thanks.

 

Take it to a radiator shop and get a patch soldered on. To keep it from happening again leave your gas acap a tiny bit loose or drill a tiny vent hole in the cap. This keeps the tank from pressurizing and flexing. YMMV

 

Google around for more information on where to add additional metal. The tank will likely crack in additional spots. There's a picture of where someone had a radiator shop patch multiple cracks with copper patches. Image might be on Pelican.