Got some coolant sealant tablets from dealer (6 in the package). Do I add all 6 for my 2005 Impala 3.4 v/6? One guy said all 6 mainly used in the Northstar engines. And... where is the heater core located, can I replace it myself or is it that bad of a job. No leaks but has the slime on the windows when really cold and winter time...hah! Windows can ice up inside the car...sometimes, not all the time. I know it's best to take some coolant and then mix the tablets and once all dissolved then add to the overflow tank. Only has 48k on it and runs ultra smooth and quiet. Thanks !! OH. ANY youtube on a core job??