So your intimate knowledge of the maintenance servicing of 769 (and therefore 319's) is to blame Northern for lack of preventative maintenance?319's have always had traction and door failures since they were first introduced down South, from that aspect they will never change, but to blame a TOC in that particular way is incorrect before the full facts are known.
As far as the passengers were concerned, it's irrelevant whether Northern or anybody else did any essential work, the fact is that the service suffered badly because nobody did and it was Northern's reputation that took the hit.
That's despite the actual known facts that the Class 319 fleet (before some were changed to 769's) didn't undergo door overhauls as part of the ROSCO led (that's the owning companies to the uninitiated, in this case Porterbrook) C6 overhauls and Northern have been trying to "nurse" the door header gear for the best part of 7 years now whilst someone comes up with the equipment to "modernise" the door header gear?
I am very familiar with the 319s working much harder than they ever do on short slow-ish runs in Lancashire. Northern (and Porterbrook) are quite familiar with BR MKIII door designs - think classes 150 (from 2011), 321 (from 2004) and 322 (from 2011), so the 319 doors weren't like something from another world. If between them a decision was made not to push for an overhaul, that's another 'feather' in Northern's cap. I'm imagine that the maintenance crews felt that their management had given them an impossible task.
As well as the fact that the ROSCO decided to fit diesel engines to an EMU fleet in a new innovative way to provide a more diverse train but failed to implement any sort of support servicing from the manufacturers for said engines and that Northern have had to fight their own corner to put this in place (and I suspect most of the other TOC's have had to as well). Basically a "take it out the box and use it" scenario was handed over.
Once again, Northern accepted the trains on whatever the terms were. If there wasn't any provision in the event of them being unsuitable for service, that is another management failure.
319's have always had traction and door failures since they were first introduced down South, from that aspect they will never change, but to blame a TOC in that particular way is incorrect before the full facts are known.
I refer to the TOC by it's franchise/service area name i.e.
'Northern', whether at any particular instant it was Arriva Trains Northern / Northern Rail / Arriva Rail North / Northern Trains, it seems from so many people here far more intimately involved with Northern in one or more of those guises that despite the changes in the company at the top, TUPE ensured that some aspects of the culture were unchanged.