Mark, it depends on what you consider 'fixing'. 5 years ago, an unchecked 'tab - chlorinator' killed the heat exchanger on one of our pools. The homeowner is in the automobile business and sent it out to a radiator repair place. Their solution was to fill the bottom 2 pipes with solder. It worked up until last season, when we replaced the entire heat exchanger. The way he had it 'fixed' closed off 2/5 of the exchanger, reducing it's BTU's while not saving a $.01 on the gas bill to run it (I'm sure that it's efficiency dropped ), and he replaced the exchanger ~4 yrs later (I don't have any 'hard #s', but I'm sure that replacing the exchanger from the start would have saved him some $).

So, yes, it's been done, but the guy who has had to work on it believes that John and Brad are 100% correct, you will be better off 'biting the bullet' and replacing it (and keep an eye on your pH in the future )