This guy has the whole issue down to a "T". What to use and how to do it. These two vids are a must see for anyone flushing and replacing coolant. This guy seems to really have his act together.
What coolant to use:
https://www.youtube.com/watch?v=EMkoxlm6mzI
How to flush and change coolant in a Boxster:
https://www.youtube.com/watch?v=whc8e6baACw
Seems like good old plain simple Prestone is the way to go.
By the way, that idiot "Scotty" on the YouTube above has to be the most annoying creature on the face of the earth. How the heck does anyone watch him at all?