Longevity? I think it is because I eat a lot of granola. I am not that old,
but my vanagon is (for a vanagon) and after all I keep my Vanagon alive.  :)

Most in this thread are talking about the engine only. My engine has
267000kms on it and has never had surgery. I have posted details before.
Regular driving, ensuring that it warms up completely, oil changes every
5000kms (consider it the vanagon's granola or carrots). Attention to coolant
and maintenance are really important. Certainly adding anything that
decreases electrolysis will help too. 
I believe that maintenance is key to the whole of your vanagon whether you
eat granola or not. There is more to longevity than the engine.

Please no flames, they might burn my granola and that would make me upset.
Then my vanagon may not get the attention it needs either. :(

Bj�rn ;)