It's just like any good 1/8 scale...external plastic case comes apart like in the manual...then you have the diff case itself...4 phillips screws to remove the diff crown gear/ cup and you've opened the diff...
Remove all planetary gears, etc...clean grease off all parts...re-add bottom gears...fill with silicon diff fluid...1/2 way...add rest gears...fill rest with fluid...to top of top planetary; too much will lock them in a bad way...test b4 re-install.
I use 30-50K front and rear for a limited slip (it's not locked...), but If you race some you might wanna go lighter...I have run 30K front 20K rear...depends on how you run...some will say 10K or 7K...
some of the sponsors like on the left should carry an array of silicon diff fluid...If not I know Daves motors does...