Spoke to the previous owner, as expected, he's a nice guy and looked after the car as per the invoices, receipts, service history etc:
Here is what he said:
"Hi Adrian. That is upsetting and I'm very sorry that you have been landed with such a bill. I have never seen the engine, as it's all tucked away in Porsches and I'm not a mechanic so don't have the ability to look. Is it worse than other cars of the same age? I only just put £1500 or so into it for the service etc. So you transferred the warranty over and they still won't cover any of it?"
"I've always been very careful to keep the oil topped up as the guy that sold it to me said these engines use a lot of oil. He said a litre every 1000km is not unusual. Plus the flaring when you start from cold. Sounds like your guys disagree. I've always done whatever work is required and then some - when one rear shocker went I replaced both to ensure no differential in strength. When one coil pack went I replaced all of them for the same reason. It is very disappointing that the engine is like that given I've always exceeded any work required. Would the corrosion/boring lead to breakdown? If so then the warranty would cover it. Once again I'm very sorry but I genuinely did not know about these issues and wouldn't have done until pointed out, or breakdown, which is what the warranty is for."
"My apologies again, I feel bad that this has happened. Persevere with the warranty people and hopefully they'll come through. It's what they're supposed to be there for at the end of the day."