Iskerbibel is right. My experience with these radiator stop-leak additives has been negative: that is, they don't work, at least not for long. Years ago I had an old Toyota that developed a small radiator leak. None of these products worked for long, and I tried Bars-Leaks, Alumaseal, etc. The car soon ended up with a new radiator.
Racing Beat recommends that Mazda rotary owners should NEVER use stop-leak products because of their tendency to plug radiators. Proper cooling is critical in these engines, even more so than in conventional engines. Racing Beat also says that if the stop-leak products are used in an emergency, drive the car gently until repairs are possible--and figure on the possibility of replacing the radiator (at least on Mazda rotaries) as flushing it may not unplug it.
Except for road and accident damage, radiators generally will not leak unless changing the coolant is neglected. These days many cars have the air conditioning condenser in front of the radiator, further protecting the radiator from rocks and stuff.
My old '88 Ford Festiva went nearly 400,000 miles with the original radiator. With regular coolant changes and the use of an anticorrosion additive, the aluminum visible when looking through the filler neck with the cap off was as shiny as new, with no trace of rust. That little car just flat wore out--I never used synthetic lubricants in it and I wish I had--and right now it rests in peace in the back 40 with that same radiator. (Soon I'll send it to the knackers. Should have bought another one just like it when I got it new in 1988; I'd probably still be driving the second one.)