at work we use redline shockproof (blue stuff), i reckon its the best box oil, u WILL notice the difference, very easy and smooth gear changes, it comes as lightweight or heavyweight grade, light is for standard boxs and synchro gearsets and heavy is best for dog boxes and rear diffs
dont quote me, but i think its around a $100 and it comes in a 4L container, but it is well worth it