Peter,

You have received good advice to do the repair.

However, when my Vanagon's head started leaking and I researched the issue,
what I found was that the most likely time for the leak to show up was with
a cold engine in winter.  Granted, once leaking, the cooling system
wouldn't necessarily re-fill from the coolant overflow tank, and air could
enter the system causing worrisome or even expensive problems if the
temperature gauge wasn't watched carefully.

Since, the leak wasn't likely to begin while driving down the highway, I
reasoned that if I could fix it with a radiator sealer, I wouldn't be
putting the engine at risk.  After reading all the bottles, I decided on
"AlumaSeal" since I figured all the powdered aluminum might be sacrificial
and dissolve instead of the cylinder heads continuing to erode.  It quickly
fixed the leak.

I am fully aware that it isn't a permanent cure, and I have had to add
 another container of "AlumaSeal" every winter (not this year yet though)
for the last 3 years, but I've gone 40,000 more miles without removing the
heads.  As predicted, the first sign of the return of the leak has always
been a few drips under the Vanagon after a cold night.  I immediately
respond with more "AlumaSeal."  I think that if you check the archives,
others have had success with "Bars Leak" as well.

Just another point of view,

Mike     '84 GL   '58 Isetta