walt spak wrote:
>
> I have put over 60,000 miles (trouble free, by the way) on my Boston Bob
> rebuilt 2.1 and 40,000 miles on my 84 Westy with green coolant and have no
> leaky head gasket yet.
>

Ah, but did you use tap water or distilled water? :-)

Let me add .02 to whatever theories are being developed.

If the main corrosion product at the edge of the heads is aluminum
oxide, oxygen is needed for the reaction to happen.  Any oxygen
initially dissolved in the water used to mix the coolant should be
depleted before too long and things should reach a steady state in a
closed system.
   But at a poorly designed seal at the edge of a head, a little seepage
of coolant might occur and a little oxygen may diffuse in from outside
as the expansion and contraction from thermal cycling moves things
around slightly.
   So now we have aluminum, oxygen, heat, and water along with dissolved
minerals which make it more conductive and may even catalyze the reaction.

Of course to keep our corrosion inhibitors fresh we should all change
our coolant, and while we're at it:
   change the brake fluid
   change the fuel lines
   change the coolant hoses
   change the blinker fluid
.
.
.

Larry A.