you can use thick oil.. i do on my monster trucks and 1/5th scale cars..

on a drift car dude all you need is to lock it..like the dude's above have mentioned, if you want some play in your diff go with a 100000 weight oil, very thick or even thicker, it will be better idf you want to play around with it, instead of pulling doe out of all the bevel gears,

i use blue-tac but oil is a good way if you want to play around with set-ups!...