I've been privately asked about the integrated garage door opener again, so heres some more information.

The garage door opener is integrated into the mirror (or the overhead control panel on the W163 ML in USA, or as a separate unit on the SLK).

To retrofit it thus you need to replace the whole mirror which is an expensive process at around £700 compared to the cost of the option from the factory.

Thus many people end up purchasing a used item from a breaker an eBay item.

If you are doing so, then these are the things to remember: -
a) Colour - there are many colours, some of which are similar - for instance on the SL there is a black variant and an anthracite variant for cars with the alcantara roof lining.
b) Auto-dim. Always buy one with the autodimming feature - you can see the auto-dimming light detector as a small circular hole in the shiny mirror backing in top corner of the mirror glass
c) LHD or RHD - the mirrors are different as they are able to rotate more towards the driver than the passenger
d) Memory - many Mercedes vehicles before about mid 2004 had memory function in the mirror. If your car has memory mirror function and you still want it then get one with memory function. You can add the one with memory function and have it enabled with Star Diagnosis by the computer - although that may not be possible to enable on the newer cars.
e) Interchangability - some models share mirrors, for instance the R230 SL, W220 S, W215 CL all use the same mirrors so although SL mirrors are rare, W220 S class ones are much more available.

There is a good article on how the door opener works and how you set the country coding and re-program it here:-

Garage Door Opener

You can use Search4CarParts to search for mercedes interior mirrors - it will look in multiple languages so you can often find better / more deals - but remember the LHD / RHD issue.

Richard