I just finished replacing my heater core -what a PITA. Anyway, the PO used a poor quality pot metal water neck on my blazer so it subsequently went south. NAPA to the rescue with a nice $15 cast iron water neck that seals like a charm. Seems to me that the pot metal cr@p should be outlawed as a safety hazard by DOT. I've ended up replacing every water neck on the vehicles I've owned with iron units if available.