Ken, well, no guts, no glory. Was home from work today, so went out and removed/repaired the rear view mirror on my '96 S500. Like yours, it has the IR sensor, etc internal to it.
I took a number of pictures so I could show you how they break.
Regardless of other postings, I would not recommend you simply pull down on it. If yours is like mine was, the internal mounting is loose from the back of the mirror glass. If you pull on it, you will break the housing.
Instead, take a small screwdriver and pry the trim piece off the miror base... see the attached picture. This will reveal the electrical connectors (one is power/grd for the dimmer, the other is the IR system) and the method of mounting. Mercedes used a horizontally mounted spring to hold the mirror into the roof bracket. This bracket also hold the Bose tweeter in the center of the windshield.
After you remove the trim piece and can see the associated pieces more clearly, pry the mirror base loose with a screwdriver. Pops right out. Just unplug the wires and you're out.
If yours is broken like mine, you can now shake the mirror and hear the broken plastic pieces rattling inside. This is not a good thing. :-)
Anyway, pry the lower housing (has the IR sensor) off the mirror head.. it just pops off. Then you can take a small screwdriver and separate the mirror head into two pieces revealing the interior and glass.
I was pretty disappointed... internally, this thing is poorly designed and made. Looks like a kid's toy. You'll see the ball mount (where the mirror head is supposed to swivel) is loose from the back of the glass assembly.
There are two metal retainers that are supposed to hold this all together... but, in my case, the tiny, weak, (did I say weak?), mounts for these retainers were broken off.... releasing the mirror internally.
I fixed mine by making substitutes for these mounts. Took about an hour total. Better than 900 plus bucks for the replacement, eh? Frankly this mirror doesn't have more than 5 dollars worth of stuff in it... Mercedes should be ashamed of this thing.
I'll post a picture here to also show how its supposed to go together inside... look where the screwdriver blade is holding the retainer and you'll see where the piece is broken.
If you want more pictures (I took a bunch) of the repair, send me your email and I'll send them to you.
Regards, KenP

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