To answer the question: Use the fact the owner replaced the broken turbo with a used turbo as a negotiation point to lower the asking price. Yes it may go sometime soon, but is there any guarantee the turbo you purchase in any car covering 80k won't go? Take along a mechanic friend or have an AA inspection carried out on the car if you're unsure. Also might be worth looking for some sort of 3rd party warranty (read the small print) although I'm not sure if they cover cars that old.
Others have questioned that sort of money for a car that age. Must say I have to agree. It's not just the value of the car you have to take in to account, it's keeping it on the road - expect all sorts of bills. If you buy an 8 year old car and it's 100% reliable then you're very lucky. There's no way I'd spend that sort of cash on a car of that age, but that's just me.
Even so, you'd need to come up with some very creative accounting to make up £7k+ worth of damage if all you needed was some bolt on parts.
Car's are written off when the repair costs are between 60%-80% (depending on insurer) on the value of the car. And I don't know where you get the £7k valuation from. The insurers go on Glasses guide to value a car, not uk-mkivs. The valuation of an 8 year old anniv is not going to be £7k+
But heres an example of a car we had wrote of recently at work.......A Mazda MX5 '57' plate, the woman who owned it had run over a suicide jumper on the m way (the third car to do so once the chap hit the road) who jumped of a bridge leaving the car with very minimal damage to the underside and some small bits of burnt skin on the exhaust. The woman who owned the car refused to take it back whatever the situation as she found it to traumatic. The insurance company said fair do's and wrote it off.
Wow, hold on a minute, was that Mazda registered as a CAT D write off? There has to be something more to that story. Can't see the insurer making a loss because of the owners feelings - it's not as if they're able to sue the suicide victim to recoup their losses. If I were an insurer, I'd have repaired the car and handed it back to the owner. Now if she felt that for whatever reason she could no longer drive the car, she could always sell it.