Last week I had the oil and differential fluid changed on my '84 380SL. Yesterday I noticed that the differential had a leak that was dropping oil (about the size of a quarter) on the floor of my garage. After looking at the bill I noticed that the tech had put limited slip oil in the diff. I don't think that my car has one and so my question is twofold.

A) Is the leak perhaps due to the different fluid?

B) Can I stop the leak by just changing back to the regular fluid or am I in for a big bucks repair?