variable valve timing hub?

Nissan Almera 1.5, year: 2003

Timing chain on my Nissan Almera got stretched so I agreed to paying £530 for the timing chain but just got a call
from garage saying the "variable valve timing hub" ceased up which caused the timing chain to stretch in the first place.
Fitting a new variable valve timing hub cost £830. Does anyone know what a variable valve timing hub is?
Not sure if it's worth spending £1360 considering the age of the car.
Thanks

Nabile
September 2009