FranD,

Well, all I can speak to is my experience over 30 years.  I use it in
all my vehicles: MGB, Chevy Blazer, Saab, Audi and my Vanagon.  The
first time I used it in my '84 Westy was ten years and well over 100,000
miles ago (same engine, now at 200k mi., but will be replaced soon due
to excessive smoke when cold).  I have added it every two years when I
change the coolant (except now I use Dexcool and will add it every five
years).  I replaced the heads a few months after I added it the first
time, so it doesn't work miracles, but it might buy you time.  I have
almost 100,000 miles since the last head replacement, and they are still
not leaking.

I stick to the statement that it hasn't hurt anything, and I still am
getting plenty of heat out of my front heater (the rear has been
replaced due to the usual severe rupture), so it hasn't clogged it
either.

If you have any doubts don't use it.  The next problem you have you will
blame on it!

Start saving for the only proper fix, head gasket (and possibly head)
replacement!

Stuart