The diffs come with grease which will work fine to start with. Then get my cross pin converstion kit.
I am using 17mm hubs to narrow the truck up some. The proto truck had shorter arms but I used extended 23mm hubs. Also, the 17mm hubs are half the weight of the 23mm's. And Pro-line finally released offset 17mm wheels and I like them.
http://h1072672.hobbyshopnow.com/pro...prod=PRO269202