It all makes sense and I mostly agree with what you said, however there still is a point where a car isn't economically viable to start fixing and you then start throwing good money after bad. Like you said, spending £1k to repair a £600 car is more economically sound than replacing it with another £1k car that requires more work. Given enough money, pretty much any car that develops a fault can be fixed, however doing this every time isn't necessarily economic sense. Finding that point where its not worth fixing it is always be tricky without hindsight at the time of the decision. In effect, its a educated gamble to either fix a car or replace it. Like most gambling, the risk can vary on many factors.
In the case of my vehicle, it's past track record of reliability has been exceptionally poor. In the past 4 1/2 years of ownership by my parents (who had it from ~15k to ~113k), it has had 15 or so different faults (road springs, egr x2, turbo, injector 3 wiring, alternator, etc, etc), of which a large number of them required the services of the main dealer. In the year I've had it (just coming up to a year next month - done from ~113k to 127k), I've already had 5 different faults (ABS wiring chaffing through, air con recirc flap motor, airbag warning, thermostat, now swirl flaps). So I reckon the risk of keeping and having another major problem after another is potentially fairly high.
Even worse, the swirl flap rod has a date code stamp of 03/07, which means they have been replaced at least once since the car was made! Its not good when common faults that have been fixed with supposedly uprated parts start failing again. I was hoping that the car would be at a point soon where nearly every common fault it could have had, has been fixed - thus limiting the amount of repair time+money needed. So this latest fault happening again has dented my confidence in that.
The risk of changing also depends to what I change it too. I know any car has/can have trouble, however some models still have particularly less problems (or cheaper to repair problems) than others. The other factor in the cost of repairs, for me, is the ease of repair. For example if something in the fuel injection system fails on a n/a petrol, generally I would be happy to fix that myself with my average DIY repair skills, thus making it a very cheap repair. However if a common rail f/i diesel system fails, with the pressures, tolerances and complexity involved, its something I wouldn't want to attempt to repair myself. So thus, as an broad example, changing to a N/A petrol would be less risk than potentially keeping my car.
I really don't know how long I will keep this car. I like the car a lot and want to keep it as long as possible, however the intention is still to run it until its not worth repairing - I certainly don't have an emotional attachment to cars any more and wouldn't have a problem to take it to be chopped/broken up if needs be. The timing all depends on what faults happen when. If the DMF/clutch fails and is replaced then shortly after have a road spring go, then I would be fairly happy to replace the spring.
However as another example, if I have a water pump seizure (which has already happened once, so I hope it doesn't happen again!
), which is repaired and then shortly after the turbo blows again, I would find it hard to justify replacing the turbo, knowing that the DMF/clutch is coming to the end of its life shortly too. At this point the vehicle is pretty much an economic write-off - as it would still be worth at least around £1-2k as a spare/repair car on eBay.
Incidentally I reattached the swirl flap rod by letting gravity and oily muck hold it together, and the car runs great again. Have you had any incidences where the swirl flaps have failed twice on the same vehicle? I guess this may be a tricky question to ask, as I suspect generally the car's ownership has changed and is many years apart before it could happen again. I'm tempted to contact the dealer to find out when the manifold was changed last to see how long it really has lasted - and also if possible, to see if it is an 'uprated part'.
Cheers,
Si.