98 STS northstar overheating 117,000 miles

have 98 sts northstar with ll7,000 miles..overheating..no smoke, no water in oil, no water in exhaust..radiator waterpump gas cap all ok..mechanic says 'head gasket'..2500.00 for steel inserts or rebult engine 3500.00..this is not an option..have gm brown six to a pack radiator collant tabs..was told to put in radiator..others say grind into powder and put in lower radiator hose..not in radiator..any suggestions would be appreciated.
William

what did you find out