Not sure if you have this option locally, but I just got my oil tank back from Pacific Oil Cooler and they bead blast and test. They can tell you if a repair is needed and if it's fixable. They also do an amazing job at cleaning and painting the tank.
See my thread on it here:
http://forums.pelicanparts.com/porsche-911-technical-forum/770954-oil-tank-unboxing.html