Just to update, in the UK ( I assume SN20 is based elsewhere - LHD car)
The driver's side mirror ( in whatever variant ( LHD /RHD) is SIGNIFICANTLY easier to do than the passenger. I think we all know that MBZ cars have a slightly different passenger mirror than the driver's side. This has different internals, it may look the same in terms of the camera, antenna etc but the main bones if how the thing is put together internally are different. This makes passenger side a complete PITA.
I tried everything to get this thing out, I couldn't work out how to get the outer casing off ( which would have made life easier) but as SN20 points out, it's plastic and to a degree, fragile, so didn't want to push it. When I say I tried everything, in the end I took off the doorcard, and removed the mirror and still could not get it out. The light basically fouls against the part that holds the gubbins for the mirror motor, it's literally 2mm of clearance that is required.
Luckily, I'm as stubborn as they come and refused to give up, in the end, I took an oscilliating tool to it and shaved off 2mm. No you're not going to see it and no, it won't compromise any structural integrity. Finally, after a lot of head scratching, sore fingers and a few expletives the old one was out, and the new one was in.
I have no idea how they change these at the dealership - but I would like to know, so if anyone has knowledge of this please post it up, because on the passenger side it's not a pop off and pop on event.
The driver's side, however, was a completely different story. I psyched myself up and did some finger exercises only to be greeted with totally different internals, the old light popped out and the new one in, I was done, dusted and drinking tea in 30 mins.
Below is the old (top) Vs new (driver side) note the different numbers, the new one seems to have a silicone seal around it so hopefully better at keeping the moisture out. Note the moisture on the old one.
It's also worth watching the following videos on youtube.