Hi I know it's a bit like asking how long a piece of string is, but when on average would the brakes (hopefully just pads) need replacing on my A4 B6 1.8T? The car has now done 21000 miles and am thinking it must be soon. Most of the miles I do are town driving so frequent soft braking. And does the A4 warn when the pads are low so the discs aren't eaten into? Thanks!