No, I haven't checked the heater valve. I tried a few days ago, but I didn't know where to look other than somewhere near the firewall and by the windshield. Then from this post I learned it's on the battery side and underneath the plastic "grill" thing where leaves and debris always collect (that spot). But I still don't know what to look for :|

Anziani, I was quoted about $500+ for a heater core. This shop doesn't accept customers bringing in their own parts. Did you get any warning signs priot to the core "exploding" coolant out into your interior?