Rebuilding heater box, replace core?

Cost me $400. to have a radiator shop recore my '72. Expensive, yes, but it fits and doesn't leak, and probably won't in my lifetime. Do yourself a favor, old style green antifreeze and reverse osmosis water at correct ratio. Distilled is next best water. Look it up if you are a Doubting Thomas.

I've always used old style green and distilled water in all my cars. I agree $400 isn't horrible if you only had to do it once.