I just recently purchased a 1984 turbo diesel 300D. It is the first Mercedes that I have ever owned and it is pretty awesome. After driving it around quite a bit this weekend I noticed that there is a medium pitched hum coming from the rear of the car. I took a look at the rear differential and noticed that there was a drip of oil hanging from the point at which the drive shaft connects to the rear differential. I thought maybe it was a bad seal or a worn bearing of some kind. Could anyone give me some tips on what this problem might be.

I am also looking for a online catalog of all of Mercedes parts. A friend of mine told me that there was a web site somewhere that had a list of all of the parts for my car. He said it was called the Mercedes Star catalog. If anyone could point me in the direction of this online catalog, It would be much appreciated. thanks!