Find out what pressure is in that hose during normal operations and what it is rated for?
For example If it's only 1 or two bar pressure I'd be arguing that no hose on the planet is manufactured to work at that pressure. They're all made for minimum 10 bar. Oil pressure on large marine diesels is about 4-5 bar but hydraulic pressure can be 3-400 bar easily depending on the application just to give you an idea.
All mechanical components are tested to minimum 30% over and above their normal operating pressure, temperature, flow etc.
What's the mileage on the car? Is this something that should have been spotted during the last inspection? Normally when a hose is beyond its life cycle it will cracking and go hard but that is well beyond its life cycle.
The information you need to find out is what is the hose rated for and what was it working at during normal operations. If working below it's design spec then you can push for material defect.
I've had Audi warranty try to get out of a few things like this before but I've proved them wrong each time. If they can get out of something, they will.
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