If you have enough money that purchasing a new tank is an option, then I'd say just do that.
If you'd rather not spend that much money you could run an extended leak test and see whether it's trustworthy or not. Set the tank up outside or in a garage, fill it up - maybe hook up a wave maker or pump of some sort - and let it go like that until it bursts or enough time has passed that you are more confident about it.