Hi
I would recommend as a matter of course changing your timming belt on a VW transporter at 3 years or 60000 miles, although some VW engines are 3 years 80000, but this would need to be clarified with a VW dealer. I always stick 3 years 60000 for a belt change, cause if it snaps it is a very expensive repair.
ATB
Colin
January 2008