Why do the cam belt and tensioners in our 2003 Volkswagen Polo need replacing for a second time at 19,800 miles?

My wife drives a 2003 Volkswagen Polo 1.4 Twist. In October 2007 at 11,900 miles cam belt and tensioners were replaced by a Volkswagen dealer. We have now been advised by the same dealer that this apparently needs replacing again, despite the present mileage only being 19,800. Her car is only mainly used for local short runs, hence the very low mileage. Can this replacement really be necessary?
It's due to lousy engineering involving plastic pulleys that fail without warning, in spite of the fact that GM in Germany used the same system in the 1990s and found it to be very short lived. Don't German engineers talk to German engineers? Or are they overruled by accountants? Yes, replacement of the belt and particularly the small plastic rollers is essential.
Answered by Honest John on

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