I agree with apache_brew, welding may be the best way to salvage what you have and guarantee no leaks. I have tried epoxy in a similar manner and it held for a while but always failed eventually.
I had some welding done last year and think I paid $75/hr. I also think based off that experience...
This may be a bit of a stretch for pressure fermentation/transfers but have you thought about trying a Uniseal? They are sort of like a bulkhead but typically used for pipes out of water vessels. They are flexible and water tight just not sure about how much gas pressure they might hold...