I'd pull the whole assembly now, before you actually need it. Pull it apart and clean all the stuff that has resided in it from day one, and look at the core and air test it. Only saying this because if it leaked before and it was bypassed but corrosion has plugged the hole while sitting with no coolant, it might test fine in there. But at least with my luck the day I would go to drive it somewhere it would puke it's guts on the floor, only if I had nice carpet, or any carpet that is.