hey guys i own a 2010 g37x sedan with 50k and i have never done a flush on any of the differentials. My question is do i just do the flush on the rear or both ?

i hear the rear is the one used for the most part on awd, please if anyone can answer this ASAP

 

You should flush and replace both at the same time. Regardless of which one is used the most, they're both used frequently, and its better to be safe than sorry. It also makes it easier to remember when you changed them, and you don't have to try and remember two different flush intervals.