Similar experience to Don - Chevelle that I dumped a couple cans of Barrs Leaks in -stopped the little bitty leak in the heater core but a couple years later when I finally removed it to fix it was a solid block inside and was beyond repair. Gave me a couple more years but I always knew it wasn't right - kinda like having diarrhea and just praying you don't sneeze - sooner or later you'll have a bit of a mess to deal with..