I think it's also worth mentioning that this is just a band aid, not a cure. Rust is cancer and if you treat cancer with a band aid then it will be out of hand and running rampant before you know it. I know repairing the cowl properly is expensive and labor intensive but take a look from under the dash, if it's the edge of your tophats leaking then you might be able to fix it from inside the car, for now at least.