I have a 2005 Envoy with 381K miles that has developed a minor head gasket problem. It's not losing any coolant, BUT combustion gas is getting into the coolant causing overheating. Note: The radiator was replaced about 10K miles ago. My question is which brand and type of Head Gasket Sealer would you recommend? (know that the treatment cannot involve removing the thermostat as it's a thermostat housing). Also, before anyone jumps in with "get it fixed with a new gasket"...please remember that it's 17 years old with 381K miles and worth about $800. Just need it to last long enough until this supply chain mess is over and dealers actually have an inventory of new vehicles again.
