I was able to figure this out so no one needs to write back. Microphone cap and lens cap come off easily with a small pry screwdriver.
For those with a 2002 SLK, it is necessary to remove two screws underneath the overhead light lens, in order to pull off the 5 foot section that goes across the windshield.
This enables one to reach the mirror to twist it off like Gabus said. It takes quite a bit of force to remove it.
Thanks a bunch for this Mercedes site, as it has been very helpful.
Also helpful was a video showing the actual rearview mirror removal:
www.buellwinkle.com/r170/default.htm