I don't know if the front 'cell' is the main or the aux tank but my forts questions would be, "Do you need both tanks?"
A few things to note" If one tank has corrosion holes, maybe the other one does too ( 25 years old) and have you seen the spot that leaks. More often than not, corrosion occurs on the underside of the tank and you can't see the damage unless you pull the tank.