I had a crack on my former rider. I roughed up the crack w/sandpape & did use JB Weld, & ordered a New Tank.
Well the JB Weld (Original formula) worked so well that when new tank came & I never installed it, In fact I just sold it here. That mower is still running with repaired tank on it.
Point is, in my case the JB Weld worked great. I did add a stiffening brace to mounting pads on that mower, which is what caused the crack to begin with.