Fast flashing is indicative of a non-functioning bulb caused in your case by poor contact---clean the bulb and socket as instructed in an earlier post. This site has the correct bulbs for your car and Pep Boys sells Sylvania bulbs that are correct for your car (Osram Sylvania manufactures OE bulbs for Mercedes and if you look at the Sylvania bulbs you will find "Osram" engraved on them). I have found that by replacing bulbs in pairs you will have fewer problems. Although perhaps overkill, for the low cost of bulbs I replace all the minor bulbs at the same time to save labor and future headaches. You can also bet that when one bulb burns out the other is soon to follow. Mark