It also boils down to selling units. I must amend my statements. In a normal world, where people take responsibility, there is no need to change the unit. Given the present state the only correct action is to replace the tank. We live in an time where people can not, for the most part, think responsibly, intelligently or mechanically. The minimal amount of prudence that would go into making sure a hot water tank, that has been under water for X amount of time, stays safe is actually beyond most people. Perhaps not beyond intelligence but surely beyond extending any extra effort. As most know I take very little seriously but in this case the best thing to do is recommend replacement. It's the only way to take the "idiot" out of the equation.