If you are considering using a stop leak, think again. The aluminum and copper particle stop leaks are "unhealthy" in a sense that they have tiny (and ABRASIVE!) metallic particles flowing through your radiator, heater core, block water passages, cyl. head water jackets, thermostat and housing, and your water pump impeller. The Non-abrasive sealants like Bars-Leak and KW work fairly well but are hell to get out of your cooling system once repaired. My girlfriend had a "tire place" work on her car while I was out of town and they put some in as "preventative maintenance". Three flushes and 2 months later and its still not all out, when I first saw the tiny brownish swirls and balls floating in the recovery tank I nearly flipped thinking that the headgasket was bad until I got some of this sticky brown "gunk" on my finger and figured out what it was. I would seriously suggest doing it right, stop leaks either inhibit flow through narrow passages, are abrasive to the cooling system, or are snake oils.
Best of luck.. BTW if you dont want to shell out for a new core or radiator, you could always solder the leak