Exterior Rearview Mirror problems of the 1999 Audi A4

This is not about a particular incident but rather something that has been getting progressively worse. The exterior mirrors have been losing their reflectivity. I was told by someone that it's the silver on the backside of the mirror that is flaking off and that it happens when the temperature changes fairly quickly. I asked my local Audi dealership about this and they said it was very uncommon and would be about $75 to replace the mirror. As I drive around and as I walk past other Audis and volkswagens I notice that the same thing is happening on their mirrors as happened to both of mine. I asked a mechanic at another shop in rutland about it and he said he sees it all the time. If it's the nature of the reflective material and it's reasonable to have this happen then fine. It seems as though, however, that it's a problem plaguing many of these types of cars and a problem that Audi, or at least my local dealership, will not admit is a common failure with these mirrors.