Just finished reading the whole thread...
OD, have you established how many miles this guy has covered since taking ownership? If so would you mind posting it up for us as if he is genuinely using it to smoke up and down motorways on a daily basis then he will have added quite a few which would support heavy use of an old end of life car and also you have 50ppm deduction of you take it back.
Just like CAG, it might be interesting to establish a thread in the private forum where we can post cases we have 'WON' in depth, as this would allow others to gather information and discuss their options in a war room type environment.
Following on from what Simon said about the manufacturer not willing to offer a std warranty beyond 3 years, would it be worth contacting each manufacturer by letter/email etc and asking them if they would be prepared to stand over a car outside of their warranty and if not, why not?
It could be that some may respond on a case by case basis for cars just outside warranty, but we could also ask about cars 5 yrs/10 yrs outside warranty (particularly for the prestige brands that are still popular to buy/sell) and see what theur stance is. My belief is that none would retail them nor would they even consider a contribution, regardless of miles/service history.
Again, having this paperwork to add to a court bundle has to make a judge think twice before finding a small indy like OD here as being the big bad wolf.
Him driving on works in your favour, get evidence.
Him taking for 3rd party repair works in your favour, get evidence.
Him buying a big old smoker to use as a daily motorway hack (I presume l, evidence need please) could also be stated by you as being unsuitable for purpose as what he really needed was a small ecomobile, as new and low mileage as possible.
He choose flash over reliability and if he has racked up the miles he is responsible for taking the chance the old smoker would have held together.
2800 on a 10 Yr old toyota corolla with 40k miles would have been money much better spent and better suited to his needs.
You have alot going for you here OD and I wish you luck with it.