yes, por 15 will fix that and worse. I had to put duct tape on the outside to cover some pin holes before I used the por15 on several bad tankes. Its the most expensive and its considered the best.
be sure to follow the steps with the acid and then wash and then dry, dry, dry, before useing the final por15 sealer. tank will then be good for another 100 years. I would then prime the outside and put about 6 coats of very good grey paint on the outside to make it last even longer.
only thing wrong with por15 is that the acid wash will remove all paint.. and even if you seal the tank during treatment, it will still remove all the paint and thats not good if its a painted tank, so you must figure on repainting the outside if its a painted tank.
expensive, good and forever!!