A leaking heat exchanger in a swimming pool heater, really isn't that dangerous, it's the side effects that may create a dangerous situation? A heat exchanger only has water going through it.

Unfortunately for the owner of a pool heater that has a leaking heat exchanger, the previous answer is pretty close to accurate. I say that, because what may appear to be a leaking heat exchanger, could be a flange gasket or, especially with the type of heater that you said you have, might be the thermostat probe that goes into the front header, could have failed.

But... saying that you do, have a bad heat exchanger, that could be close to more than half the cost of a new complete heater. You have to do the evaluation, comparing to the overall age of the heater, is there a lot of rust and corrosion buildup in the bottom of the cabinet, inspect the combustion firebox, do you have broken fire tile? All of this needs to be put into the equation, as you consider the comparison, whether you should repair the heater by replacing the exchanger, or just replacing the complete heater.
normally a general rule of thumb for me, is that I really should consider replacement (taking everything into consideration), if repair approaches more than 50% cost of replacement. The advice of a nonbiased, honest service provider may be able to assist you in that decision.

I suggest you have a reputable heating contractor evaluate your situation. A leaking heat exchanger can be very dangerous, so either the heat exchanger needs to be replaced or you need a whole new unit.

Dunn Heat Exchangers Inc Heat Exchanger Cleaning Repair Fabrication

Balance chemicals in pool and replace heat exchange