Going back to the point that South Tyne Lad made, the problem hasn't been strictly engine related with the 57 plates.
7501 - 7505 (7506 for a short amount of time) spent time at Blyth Depot. Now, although Redcar depot allegedly didn't look after the 57 plates which they got for the 93/X93, Blyth's engineering is good but, the problem has been down to the lack of spare vehicles to allow these vehicles to be given the required maintenance. If they were late on the 308, they ended up going on the express routes and therefore, got a hammering without the required maintenance.
The only potential for these now would be to be split and used as spares not only in the N.E, but perhaps around the country. And a bigger problem will come when ADL stop the classic bodywork.
RE: Arriva North East: Rare & Odd Workings - February 2016