Newby here. Purchased used 2000 DHS with 41,000 miles. After about an additional 6000 miles started getting “Check Coolant Level” msg. Also, on occasion the engine startup would be rough for a few seconds then run smooth. Advised mechanic at normal oil change interval. Mechanic researched and diagnosed problem as head gasket. Advised repair could cost up to $2,500. Recommended tablets as interim fix and suggested probably better off trading in vehicle for something else. He dropped GM tablets into surge tank and worked fine for last 500 miles. After reading forum articles, understand tablets should have been inserted into hose. Should I obtain more tablets and insert in hose? Any idea how long the tablets are effective? Although I trust the mechanic with both of my vehicles, he has never performed a head gasket replacement on a Northstar engine and therefore estimated cost may be low. Any thoughts appreciated. Is there any chance it may be another problem other than the head gasket?