When I installed my GM Goodwrench replacement engine a few years ago the instruction sheet recomended adding cooling tabs to radiator. I followed the instructions. Following is a quote from the installation instructions.

"Always add Cooling System Tabs. Cooling System Tabs aid in sealing porosity in aluminum and remove silicates from the Water Pump Shaft that form from the coolant, to Extend Water Pump Seal life."

 

I have used these 100's of times probably. I was a GM tech and the northstars had a lil intake problem and when we would do gaskets we would add four tables upon completion.