1) I hear
that if the front diff whines when accelerating it is the pinion bearings. (and if the rear whines upon deceleration, it is the pinion). The wheel bearings normally don't have an acceleration/deceleration sound associated with them.
2) Pick up the diff fluid anywhere (Napa) buy you'll need to get the friction modifier from the dealership. Check out www.wjjeeps.com
for the specifics on which gear oil you need.
'04 WJ, 6" Clayton LA's, 242 SYE, 35" BFG MT KM2's, 4.56 gears, & D44a locked
'14 WK2 Limited w/5.7L, ORAI, & Tow Package