I just changed my Rear Differential Oil today with the help of this thread! My Z has 4,000 miles on it.
Thanks to SpearFish and (Jeff) Schrute for helping a brother out.
By the way, I am most likely the biggest noob when it comes to cars on this forum. I've always paid an arm and a leg to get my maintenance done on my other cars. Now it's time to do it myself and save some money! Everyone has to start somewhere.
My point is, don't feel discouraged to do this. It is very easy and if I can do it, so can you!
(I changed my engine oil a couple weeks back, that was also very easy too!)
Anways...
Here's a picture of the old rear differential oil (left side) that came from my 370Z and the new RedLine 75W90 oil (right side). Looking at the difference, I am so glad that I changed the rear differential oil now than later!
Might I also suggest using a battery powered siphon pump. I bought mine from Amazon, this is the exact one I got (there are cheaper ones): I think battery powered is easier than air pump powered. It was so easy for me to pump the new oil back in with this:
Amazon.com: Sierra Tools JB5684 Battery Operated Liquid Transfer Pump: Home & Garden
I hope my post helped. It's the least I can do! Thanks!