I had my differential fluid changed after about 1,000 miles due to a leakey axle seal and my mechanic said that the fluid was extremely filthy. He said that it should not be nearly that dirty after only 1,000 miles. Currently the car drives fine and I do not hear or feel anything from the rear end. Could this be a sign that I may have a differential issue arising?

 

It's normal for the oil to get dirty again since you didn't have the diff flushed with the first change. There is dirt clinging to everything that doesn't come out when you drain it the first time, and it gets suspended in the new oil. If you want to play it safe, change the diff oil once more.

David