I would take it right back to the dealer you just bought it from and get them to fix it. Did you get some type of warrenty?
Afaik most of the newer MB's have what are called "sealed for life" trans. So leaks are very bad because you cannot really add fluid. You can't just break the tab and dump some fluid in you need to know the temp of the fluid to get the level right. The level is extremly important for shifting.