Most of us use phosphate-free antifreeze religiously in hopes that it
staves off the dreaded head leaks.  Still, I've known vanagons that had to
have head replacement at 50K with Volkswagen antifreeze and others that
used whatever was on sale and went over 100K, so there are no guarantees. 
Still, since Prestone now has a phosphate-free antifreeze at a reasonable
price (comes in a silver container instead of the phosphate-containing
yellow container) why take chances?

Bill