In suitably contrary style, my RST came with xtr v brakes. However, while re fitting the brake cable yesterday, I noticed that the allen screw was turning very easily. Further investigation revealed that the thread on the v-brake arm to which the cable fixes had stripped out.
My v brakes are 4-5 years old, but this was a bit of a shock. Good job the failure occurred in the garage and not half way down Holme Moss!
I have ordered an XT rear off Wiggle, because in these straitened times, £23 for a good solid brake beats £60-odd for a fantastic one!!!