Originally Posted by wstar

Any quality synthetic 75w90 is gonna be fine in the diff. Personally, I like Royal Purple for my diff, but I doubt it makes a huge difference between the good vendors.

On the 7AT: the official Nissan stance is that the fluid inside the thing is good for life and never needs any changing. However, at a mere ~18K miles my 7AT fluid looked like it was about done for. Keep in mind I drive in a lot of summer heat and I use/abuse the 7AT pretty hard. I wouldn't think it's wise to go more than ~20-30K miles without changing out the fluid, unless you always drive it like a grandma. A little 7AT fluid every 20K isn't a big budgetary concern anyways.

Any quality Nissan dealership can do it for you, but you *do* need to use a dealership because only they have the Consult-III diagnostic tool to tell them the 7AT's internal temperatures to set the fluid level correctly. I really have no idea why Nissan went down this path of trying to make the fluid a "good for life" item, I can't even imagine an angle it makes sense from business-wise. It might have mostly been that this tranny requires the aforementioned precision refilling and they didn't want to say "You have to change this fluid regularly, but you can't do it yourself", so they opted for a very long-life fluid.