Given 'lifetime' intervals of a lot of fluids these days, I still will continue on 30K intervals for tranny/diff. Has worked fine for 350+K accumulated miles in my past 3 vehicles. My weapon of choice has been Redline synthetics for this use case. Brake fluid is a bit of a meh to me, and is more about age then miles. Aggressive folks will change it every 2 years. For low mile vehicles, 4y works fine. People often forget about clutch fluid while at it, and to me that is more important as I have seen more slave failures in my lifetime then brake master.
Nissan OEM fluids, in my 2010, are not full synthetic IMHO. Recent cold spell on the east coast felt like molasses for the first 5 minutes of shifting...so MTL 85 will be going in next fall, well short of 30K
- b