Some advice please!

Ok guys, need some advice.
Bought a Fiat Brava about 2 months ago. About a week after I bought it the airbag light came on. After much running about a garage has said that the
ACU, Wiring and Clock spring needs to be replaced (this is a second opinion). Cost of this will be something like 400 +VAT and Labour.
The car is still under warranty, but obviously the garage I bought the car from is not too keen to pay up because it would affectively mean they made no profit on the sale. If push comes to shove, do they have to pay?
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