Just had the dreaded text today informing me basically the above - 17 plate A5 (3.5 years old, around 23k miles in) which I've 'owned' from new (leased from new, then bought). Was completely flabbergasted to say the least - they basically wanted to charge me 10% of the cost of the car from new to fix this one part?!
I called them and spoke to the lady at the dealership, politely querying how a part could wear out so quickly - I didn't mention Sale of Goods Act or anything along those lines. She was very receptvie and said she'd see what she could do. She came back later saying she *thinks* that they can reduce the cost to me by 80%, so still £700 but a lot better than £3.5k!
Not best pleased overall.