Welcome to the site.
You wont find many fans of any stop leak products around here. Stop leak does not know the difference between a leak, or a small water passage that if plugged could reduce the ability to cool.
Radiator, and heater core passages can be fairly small, and if they get plugged up with tis stuff, you could create an even larger problem.
As far as the leak is concerned, be sure that it is not a heater hose, or one of those pesky quick release connections.
Since you mention the leak on the driver side, it might be something else.
You should inspect the intake and be sure that the water is not running from another place to the rear of the engine, and it only looks like the leak is back there.
In a worst case situation, there is a freeze plug on the back of the head, and if this has reached the end of its life, it as well as others will have to be replaced.