Are you sure?
C4 exams are mileage based, but C6 bodywork exams are usually time-based.
Page 4 of this document states as much:
https://www.porterbrook.co.uk/rolling-stock/links/6yearplan.pdf
Nope. System shows miles to the exam. I'd rather go off engineering principles than a PR document.
Vinyl!
Its for uniformity. The franchise has until 2021. Personally i'd leave the units white and have light grey diagonal stripes at the coach ends..basically the opposite to what the 700s and 365s have. It saves having to paint the whole unit. ..plus of course the blue doors. This can all be vinyl.
The fact that its deemed as a waste of money to have a form of uniformity is short sighted and is taking your eye off the ball....and besides..the franchise MAKES MONEY.
Viynal won't create a seal like paint does. Plus viynal comes off when you clean off graitti so it's not a sensible solution.
As for shouting the franchise makes money. No it doesn't. Currently Govia is paying more into the franchise than it gets awarded due to peroframce issues. Remember 1000% of money goes straight to the DfT with GTR awarded a pre arranged fee. Hence ALL spending has to be authorised by DfT.
As for making every uniform, what's the point when but the time your finish it'll time to change things? And it's not cheap. Viynal a cost is around £10k a coach and painting is around £15k. Don't forget the Down time for doing this meaning you need to short form trains in order to get them all done. Its not as simple as you make out.
Basic maths here, for the Southern fleet viunalling the whole fleet of 1223 carriages (took the 32x 377 for SE off) would cost £12.2m for viynal or £18.4m for painting. Hardly petty cash. (basic maths too). Note the Thameslink and GN fleets would be a similar number and all that money would be wasted within five years! Can you explain why it's worth spending tens of millions just to make a uniform fleet that will properly require changes at time of completion anyway. And making things uniform is not a justifiable excuse either. Especially when to complete the work (if you could magically start tomorrow and keep the same pace going until the end of the franchise in 2021) would require an extra 6 units a week stopped (technically it's 5.88 units). That's a fair amount.
Well the doors of the 313s are currently being repainted (a nice new coat of FCC pink), and the interiors are being touched up, so clearly we have some kind of paint facility somewhere (presumably in Hornsey).
It's not a major thing but it just yet again makes the whole operation look a bit sloppy and half arsed, a bit like painting half way up the stations, though I suppose we best not go in to that again..!
Full unit painting is not available on GTR, hence why units go elsewhere for it. Door painting along with viunalling or small paint patches are an entirely different concept.