1981 -to- 2008 and the belt is still intact. Granted this means that it was stored in a reasonablr environment, but even so, if it did break it was a $.10 fix and easy to do. Belt drive was always a great method because of the mechanical isolation. These days, in the throw away world, a belt will cost you $3-$10 if you find one. Why? Because they can.
The one big enemy of the rubber belt, or any rubber, is the modern day ozone air "cleaners". Many a fine open reel tape deck have been destroyed by these "improvers" of life.