I used PRC Proseal from Spruce to fix my leak,,,I have many years experience with this brand while working for an oem,,,I have never seen it not set up if mixed properly or get soft after it has set up. It cost a good bit more but I didn't want to rework the leak again so I spent the money for it. These tanks were my first experience with flamemaster and probably my last. My opinions only,,,your results may vary...