Hello Craig,
I'm very much with Steve on this, and I'm sure this will be covered under warranty. We must take it that the coolant level in the reservoir is dropping - significantly? if some is finding its way onto the road. We guess you are topping it up with the correct type and concentration of coolant.
Kind regads,
Gareth.
p.s. The radiator on our A3 became perforated (not due to damage) many years ago when fortunately it was just within the 3 year warranty. That as replaced at the dealer without charge.