experiences with radiator stop-leak?

["G. Benedikt Rochow" <rochow@segosf.hlo.dec.com>]

As the drip rate of my '84 5kS is quite low,
I'm wondering about using a stop-leak product.

I'm interested in any positive/negative/neutral
experiences (and theorizing) on the following types
of products:

-"Gold Seal" radiator/block sealant, requires draining,
flushing with water, filling and letting sit with sealant/water
mix, draining, flushing, refilling. "Not compatible with antifreeze".

-"Bar's Leaks" small amount of liquid, to be added to warm coolant.
followed by running engine for 15-30 minutes. "Seals all
[...], aluminum, and plastic radiators and [some other water-tank-like
things]."

-"Porter Seal" (?) looks like coarse ground tobacco, to be added
to coolant, (or mix with water to make a paste to apply from the
outside :), "mechanics' choice since 1915", (C) 1937,
"also seals aluminum"

TIA,
-gbr