Hi Topgun, welcome to the club
Sorry to hear that you've had to pay out £439 for the repair of your stereo.
I have just been on the phone to Lexus dealer about my stereo. Last night it came up with the dreaded err3 message. When I spoke to the service dept, they never mentioned the extended 1 year warranty and I got the impression they were ready to give me a quote for the repair work. But before they did...I jumped in and said that I'm told the stereo was still under warranty even though the car is now over 3 years old. She seemed alittle surprised to hear it and asked where I got this info. from. As soon as I mentioned Lexus Customer care,

the conversation changed to...no problem, we'll have one for you in about 3 weeks and it's all under the warranty.
I would suggest that you rind customer services and tell them about it. As the stereo is still under warranty, they shouldn't be charging you anything.
Good luck
Ifraz