(23 Jul 2017, 12:30 pm)mb134 wrote I believe that 7509 being a 'spare' came from it being the last to be refurbished, and that it was only branded a few weeks after entering service. I think, if anything, 7509 was one of the most reliable performers, certainly I don't remember too many issues with it.
I think, if you look at the amount of time 7509 spent on the X21/22 compared to 7518, it's clear that 7518 was the 'spare' vehicle.
From my limited experience of them, the only one's that seemed to struggle were the ones that got killed on the X93, whichever 57 plate I had on the X21 yesterday certainly wasn't struggling.