Mark: I have usually used the Prestone corrosion inhibitor with water pump lube. It is about 8 to 10 ounces. The important thing is to carefully read the label to ensure compatibility with glycol antifreeze.
I also do not use the stopleak versions as I see no need to plug up any thing. There are a number of products out there. The last time was also Prestone but was sort of polymer based material but it was compatible. I do not recall exactly what it was called. Perhaps some chemical types like Paul S can enlighten us on the stuff. I will look it up at the store the next time I go.

It was on sale at Canadian Tire in Canada and was the same price as what I usually get, however it has a much lower voltage now almost 1/10 of the normal ~0.4 Volts. To me this means the corrosion rate has to be way, way down. One thing is to first make sure you have room in the overflow tank, I usually take some out with a soft drink PET bottle with the slide pop valve. Like a turkey baster, and suck it out. I then keep it tucked in behind the battery and during the next year add it when I can. I lose almost zero liquid. I have lost a bit when I have removed pressure cap and engine was not cooled off sufficiently. I did lose some when I changed the top hose but this was because I spilt the container I was catching it in.

Cheers,

--
Sheldon