Here's a pic of what it looked like from the outside...
Here's a pic of what it looked like from the inside...
So after doing some research and realizing that this mirror cost over $850 new from Mercedes, and used versions were selling for between $200-$300 on ebay and from the parts "recyclers" I decided to try to fabricate a more cost effective solution.
I realized that GM cars (and most domestics) simply attach the rear view mirror to the windshield using a steel foot attached with a 2 part cyranoacrillate adhesive. The mirror just slides over this foot and is tightened down with a set screw. So I set off to find a compatible mirror, and ended up with a 10" GM mirror. Using my wholesale parts connections it cost me 13.99 for the mirror and 4.38 for the adhesive. - Using the permatex stuff specifically designed for attaching rear view mirrors to windsheilds.
The next step was how to make this look as if it had come from the factory. Once you pop the rear view mirror housing out of the headliner, and disconnect the electrical connector, you will see that there is a large portion of the headliner missing from the center section of the headliner with it out. You will see that the original rear view mirror "Arm" which holds the mirror to the bracket that attaches it to the headliner is held on with a 19mm nut. Using an open ended 19mm wrench, turn the nut a couple of turns and then you are able to remove it by hand. You will quickly realize that you have to cut the electrical connector off of the mirror side to get the mirror off. Once you do all that remove the nut, and several washers which hold the mirror in place.
When you get the mirror off you realize you have about a 3/4" diameter hole in the housing where the original mirror arm came down from off the headliner. What I did was simply make a cheap plastic plug out of a bottle top, sliced with a razor blade, and held in from behind with a piece of gorilla tape. (all easily reversible). You have to put this plug between the metal bracket piece and the outer plastic shell of the mirror bracket. It will be obvious if you attempt it. Once the plug was in place I proceeded to snap the mirror bracket back into the headliner, without the mirror. Here is a picture of what it looks like from underneath. Mind you, that with the new mirror in place, you have to look from almost directly underneath to see the actual plug in question.
Now it's time to attach the GM Mirror to the windshield. First thing to do is determine the position of the mirror. You only get ONE shot at attaching the little foot to the glass - AND the glue sets remarkably quickly, you do not have time to reposition it or change your mind, once its on, you're going to have to soak it in acetone and use a razor blade to remove the foot very carefully in order to not break the windsheild, and especially on a 500sl you do NOT want to do that.
That having been said, what I did was take the mirror and hold it in place where I wanted it to sit. Leave the foot on it, and mark the windsheild - i used a wax pencil, so you have a location for the foot. Once you are SURE that that is where you want the mirror - mind you there is some adjustment in the mirror so you can always readjust it as needed, take the set screw out of the mirror and remove the little metal foot, that is what you are going to be gluing to the windshield. Make sure you note the orientation of the beveled edge, because that is the only way the mirror will then slide on.
Take a razor blade and scrape the windshield at the spot you are going to glue it. Open up your glue package and the first stage of the glue is in the form of a little wipe. wipe it on the windshield and on the correct side of the little metal mount. Allow it to dry (the catalyst is suspended in alcohol so it dries quickly). Once it is dry open the tube of glue and put a couple drops on the metal foot, do not soak it, a little goes a long way here.
Then it's time for the moment of truth touch the metal foot to the windshield. Like i said you have basically a couple seconds if that of working time here. If you need to reposition make it FAST. You will feel the glue react and the foot become immobile. Sit there and apply pressure for a couple of minutes then let go. Now go get your favorite beverage of choice, and take a break because you have to let the adhesive cure for a while before you can actually attach the mirror to it. The instructions said at least 15 mins, but I waited an hour.
This is what the foot will look like attached to the glass:
Once the glue has cured, it's time to attach the new mirror to the foot. Slide it over, and tighten the set screw.
Here are pictures of the final result. I don't think anyone would question it's presence in the car, unless they were an MB Purist, or performed a through inspection of the headliner underneath the mirror.