That is way too early for an SC to fail. Who knows though, it could have been something simple and the dealer just decided to rip off MB for the cost of an SC. I believe your car uses the M45 model of SC. There is an oil fill port you can check. You can buy Eaton SC oil for a lot less than if you go to the dealer. Many people use the stuff from GM because it is the same as what MB relabels. With that said, you should not have to add oil on a regular basis unless you have a problem.