I can't speak for other depots, but I've been involved in 4 separate blocks of training & I've only lost 1 run (out of 20) due to a fault. I lost 2 others with maintenance, but this was overdue/over running exams, rather than out & out failures (in fairness, one set failed catastrophically on it's way2eastfield, not long after we took it down to Perth!).
I'd like to think some of the issues with the training trains were due to it being a learning curve for all of us (including maintenance). Maybe wishful thinking on my part! The sets were, in no way, fit for passengers-cosmetically, the coaches were very poor inside, although the Classic I was on today was fine.
I hope to see more refurbished sets very soon - we need them Yesterday....I've not actually been 'close up' to it, but some of my hard bitten & cynical (sorry) colleagues had a look inside it & very pretty impressed.
On another note, I see the 1255 Inverness to Waverley is a 170