I have worked on many systems that have been stop leaked. Bars-Leak seems to be the best, but I only reccomend it in the case of a leaking heater core. I have seen many heater cores plugged from over use of stop leak. If you need a heater core anyway, NBD, but if not, you may cause yourself more problems then you had before.
That's just my opinion and if you ask five mechanics, you might very well get five different answers.
My Audi froze solid at O'Hare a couple years ago. After much effort I finally thawed it out, and the radiator blew steam from everywhere. I put in stop leak and it stopped leaking. I put in fresh fluid with stop leak then, and again this fall, no problems so far. Not the preferred situation, but I don't want to invest in a new radiator for a car with over 200k and 13 years behind it. My daughter only drives it around town anyway. Of course, I put 1000 miles on it this weekend as my wife has my 80 while her 80 gets a touch up. The 80 is a little more prone to cooling problems than my old Audi, but I'd try it.