here are a few quotes from the owners manual.
 
PG. 63 -COOLING SYSTEM
The cooling system is sealed and generally requires little attention.
      (WRONG ANSWER!! I say check it often - at least every weekend)

 PG. 64 
Use "any" quality phosphate free anti-freeze containing ethylene glycol.
 THEN it says 
Anti-freeze, other than specified by Volkswagen , may cause corrosion of the 
cooling system, leading to engine overheating and damage.

And more....
THEN I went to www.prestone.com---to the frequently asked questions and read 
this-
Q: Does Prestone� Antifreeze/Coolant contain phosphates? 
A: Some European automobile manufacturers request that a phosphate-free 
antifreeze be used in their vehicles. This issue is related to the extremely high 
mineral content of the water in Europe. If you were to mix an antifreeze that 
contained phosphates with the type of water they have in Europe, it may produce 
deposits that can settle in the cooling system and promote corrosion. 
However, in North America we do not have this type of water problem. Typical North 
American coolants have contained phosphates (which is part of the corrosion 
inhibitor package) for many years. Therefore, the question of phosphates is a 
non-issue here in North America. <A HREF="http://www.prestone.com/products/13.htm">Prestone� Antifreeze/Coolant</A> is completely safe 
for use in both foreign and domestic vehicles. For those consumers who would 
feel more comfortable using a phosphate-free antifreeze, our <A HREF="http://www.prestone.com/products/14.htm">Prestone� Extended 
Life 5/150 Antifreeze/Coolant</A> is phosphate, silicate, and borate free.