71 240z auto trans. This summer I installed all of the urethane bushing at the rear of the car. ALL of them. Since I had everything apart back there, I went ahead and dropped the differential so I could clean it up. I also replaced the diff fluid while it was out. It never leaked before i removed it. After I put everything back together I noticed it would leave a drop or two on the garage floor, but I didn't worry about it. Over the last few months the leak is slowly getting worse. Maybe 10+ drips now. I got under the car today to figure out where this leak is coming from. It looks like its coming from the top of the diff, definately higher up somewhere. It's just really hard to see much because of all of the brackets and things in the way. I just can't get a clear view. Any ideas before I start taking things apart? THANKS!

CK breather https://www.google.com/#q=datsun+differential+breather

If you remove the passenger rear wheel, you should be able to get a good look at the breather.

When I last filled the diff, it was out of the car. I figured if I filled it while it was on a level surface, it would be fill as if it was in the car. Well, after some heat and cussing, I pulled the fill plug. About 1/3 cup of diff fluid spilled out. It was obviously overfilled. Hopefully that was the issue. I guess I'll find out soon.

If you get to much in it will just come out of the breather, and even when you have it properly filled it still will come out of the breather, just not as much.