I saw this thread start (again) last evening and, couldn't wait to see
the response.
Hear again is a living testimonial, to Bar's Leak use.
Head seals weeping about 2 years ago, dumped a small bottle of Bar's in
my reservoir, and the leak stopped.
Let's see, that was about 41,000 miles ago, and have experienced no
overheating and no reoccurrence, of the head water jacket seal leak.
I would say, that if your vehicle has big miles on it, and the cooling
system hasn't been maintained,  the chances of the radiator being half
plugged with corrosion, prior to using any leak stopper, will more than
likely finish the radiator off.
My theory is, if the radiator was almost ready to die so what?
You would be buying one soon anyway.
The process just got kicked up a notch.
In closing, all I can say is, it worked for me.

Later,

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Terry 85 GL