In reply to maybe_si:
I'd go with keeping it too. Given that a very quick auto trader search suggests £3-3.5k in value there really isn't very much more value to lose. 1.5 years of saving £200 per month and you’re at break even point, even if you get nothing for the car, and after that it’s all totally in your favour.
My last ‘climbing car’ had a whining turbo for the last 3 years and 50K miles, and I drove it with the principle that when it blew I’d scrap the car. In the end I moved countries and had to get rid on the car quickly, so it went to one of the car buying companies for £600 with the turbo still whining.
Admittedly in that time I’d fixed numerous minor issues that would have started to make it less cost efficient; machining a component for the window wiper mechanism and repairing the wire on an ABS sensor meant that I didn’t have to buy new components, and I disabled the fault that the turbo caused; all of which would have cost a fair bit if I hadn’t been able to do them myself.
The things to watch out for are high cost things that go wrong with age.
Modern Diesels have injectors with a defiantly finite life, so some of the stratospheric numbers you see are maybe a thing of the past. You’re looking at £600+ plus labour if they fail. Also consider the turbo. This should give you some warning before it fails but can be a £1k fix, so keep up the regulars servicing so the oil is fresh.
I’d suggest being dispassionate about it, sitting down and working out the point at which you’ll cut your losses with running repairs (I.e. if I get a bill for £xxx, I get what I can for the car and get a new one), and stick to it; saving the money every month towards the day when the old one dies.