l know it's not a valid example to use cars windshield but if you or someone happened to noticed that small crack from a rock expands and especially when weather changes from cold to hot or vice versa. I've had to replace mine couple of years ago. I know car's body flexes and wind plays a role as well, but lets be honest what surity will you have after you use the glue especially since the crack is towards the top of the tank where there be some waves, air and light temp? then again nothing can be garunteed and nobody knows the futre; if you feel comfortable going with it by all means do, we are just providing our opinons/suggestion.