Yeh, if you take out the center diff you'll see it's basically a gear screwed on top of a cup. With the gear side up, remove the 4 screws holding it together on the face of the gear and gently separate the two halves. If there is a gasket, be very very careful not to damage it when you lift it off, use a knife and be very gentle, you'll need it. OK, now you see a gooey mess and 4 spider gears (or not a gooey mess if you are lucky, just a lightly oiled set of spider gears
). Take the gears out off their litle shafts remembering or noting the order of any washers and such. Clean out the diff case and the gears as best you can, you don't need to be spotless. Now reassemble those gears on their shafts and drop them back in. Now take your 50,000 weight silicone diff oil (ask your hobby shop or look online) and pour it in, or rather squeeze some in, since you can't pour 50k, it's very thick. Let it settle for a few minutes, add more if necessary and wait again if necessary until you are just at the top of the spider gears, now replace the gasket and reassemble, using a blue (medium) threadlock on the 4 main diff screws, while catching any silicone that spills out.
That grub screw in the side of the diff is only needed when fully disassembling the diff, leave it in place throughout this process.