The heater core in my 2001 Tracker ZR2 failed at about 100,000 miles. A new GM parts heater core was installed by the local Chevy dealer. This core failed about 10,000 miles later another new GM core was put in and it also failed at about 10,000 miles. The Chevy garage then put in a non-GM heater core and this one also failed as did the next one. Both the Chevy service people and myself have researched the heck out of this with no positive results. Everything we can think of has been checked. There is no head gasket leak or any leak of any kind from the cylinders into the coolant system. The cooling system has been completely flushed and refilled with fresh coolant every time the core was replaced and all the electrical grounds have been checked and rechecked. Does anyone have any ideas about what might be happening?

Help!!

Umichdiver