Given the labor to get at a heater core, do you guys test new ones before installing? Just sitting here and thinking about this job... I figure I might plumb up the new core to an air compressor, give it 10 or 15 psi or more and submerge it in a bucket of water, watch for bubbles. Good practice or am I being too paranoid? :eyerole It's an ACDelco service replacement, made in Mexico I think.