There are a number of threads on MBworld and others on this. There are a number of OEM 12VDC fans to fit. If you can get to yours, write down the number and do a Google search on it. From what I've read, this fails often and the Japanese replacements are longer-lived and much cheaper (~$20).

BTW- I think this fan also cools the stereo amp in the passenger floorboard. It will fail too if the fan goes...just sayin'.