I own a 2005 Octavia L&K hatchback . While driving in a heavy rainstorm  I smelt smoke and noticed that my mirror was turning to a tan colour. I fiddled with the mirror adjusting knob and the smell went. When I got home I waited for the rain to stop and examined the mirror glass and found that it was also starting to crack in the bottom left corner. I removed the glass and found that there are a pair of bayonet connectors and another pair of cables with a plug coming from the rear of the glass. there is no sign of burning to the rear of the glass. Replacements are available glass with heater  from a few on line suppliers ie AMAZON and cost about £19. They look identical to mine but do NOT have the extra short cable and plug. I contacted two local Skoda dealers and they were amazed to advise me that a new replacement glass would cost me £330. I was told that its special double skin glass with a gell between. The question is, will a £19 replacement work or will the computer display continually tell me that I have a Fault??   

it'll be fine Don't know how they came up with £330 though, that sounds like a blag to me.