Guys, I completed this repair in about 30 minutes for both sides. You'll find the gaskets for about $58 shipped from Taiwan. They are unavailable from MB. These are the only ones I could find for sale anywhere online.
Tools needed - Philips head screw driver, utility knife, small flat-headed screw driver, small star headed screwdriver/socket
(Ebay listing title) Rear View Mirror Door Cap Seal Mercedes-Benz W202 W210
(Ebay seller) atpartsonline (Feedback Score Of 677) 99.3% Positive
(Link) Rear View Mirror Door Cap Seal Mercedes-Benz W202 W210: eBay Motors (item 140448698556 end time Oct-03-10 00:28:46 PDT)
1) Slide off the mirror covers
2) Three fine-thread Philips screws hold the mirror on the body of the car. Loosen the top and bottom one, but don't remove. Push the mirror assembly toward the rear of the car and remove the bottom inside screw that was obscured when the mirror was in the normal position. Then remove the last two screws. The mirror should now be free other than the wiring harness.
3) Use a small flat-head screwdriver to remove the two wiring harness plugs from the large plug in the mirror assembly. Careful prying will free the two small harness plugs (which feed into the car door). The mirror is now completely free.
4) Remove the small star screw holding the harness plug to the mirror assembly. The mirror is now free in your hand. Carefully cut the old gasket away with a utility knife by making a circle around the wiring harness loom. Then pull the old gasket out.
5) Compare the old gasket with one of the new ones - there is one for each side of the car. The OEMs were glossy/smooth, the repro ones are matte and rough in finish, but look great on the car. There is a "square" cutout molded in the new gasket where the wiring plug/harness is supposed to feed through. I cut that out of the rubber with the utility knife to feed the mirror wiring harness plug and loom through. I actually cut slightly below the square in the new gasket, as the loom plug is slightly larger. Feed it through. Reattach the small star screw to hold the plug to the mirror assembly.
6) I then pressed the gasket on the mirror assembly and screwed in two of the mounting screws through the mirror assembly into the gasket. This snugged the gasket into place. There are reinforced indentions in the new gasket for the screws to pass through - and all lined up very well.
7) Reattach the two small plugs coming out of the car door into the mirror harness plug. Then attach the two visible philips mirror assembly mounting screws to the car body. Once snug, push the mirror assembly toward the back of the car and tighten the hidden inside screw. Then tighten all screws and slide your mirror cover back on.
Done! Sorry for no pix. I got so excited I completely forgot about documenting it. Very easy and I encourage you to do it. The parts took a couple weeks to make it to TX from Taiwan.