From time to time you may decide that stop leak can be an alternative to an actual repair of a coolant leak if it seems minor.
The Buick came in with an overheat condition, and in all actuality, the overheating situation was attributed to the stop leak built up inside the coolant system. (Radiator with goop EXPOSED @ 2:25)
You may stop a minor leak, but over time the expansion process of stop leak can restrict flow in the radiator, heater core, and many of the smaller ports to the coolant system in general.
A great product if you're stuck somewhere. Not so great if you forget to flush this goop out and ultimately repair what is leaking.
Additionally, the rusty coolant pouring out is from a lack of coolant system maintenance. Remember to check the factory specification for the required coolant change out as per maintenance.