It's hard, not being able to see the heater first hand, it would be irresponsible of me to tell you what you should buy.
Did your repair guy say anything about the condition of your heater?
Well I will be the repair guy and I was buying heat excanger and headers (was going to get the cast and not bronze) and my guess as to the reason for the leak is a freeze issue, the 2 speed relay stuck in the low speed position and when the temps went below the freeze protect setting and the pump came on it never really got the water flowing.... We do not use the heater to heat the pool only the spa a few times a year. I believe the rest of the heater is in ok shape, but if the normal life of a heater is close at hand, I would rather invest in new instead of patching the old.
Thanks