Not sure about different weights of diff grease in ball diffs tbh, as others said, AE diff lube within the diff, black grease on the thrustrace. Normally only use oil as such (of which there are different weights ie, 2000w, 3000w, 4000w etc) inside gear diffs (eg, 1/8th RallyX) as they are sealed.
I used a few drops of 40-50w shock oil on the gear teeth before closing up the box on my x2c as i'd read it makes for a quiet operation
Dan.