I have never rebuilt diffs on a losi so I couldnt tell you how to do it but one piece of advice I can give is check the manuel to make sure how much fluid to put in. over filling can cause them to leak. and under filling them can cause them to heat up.. I always fill to the top of the outdrive gear then put the cross gears in then fill to the top of the shafts.. instructions may be different but take your time here.. also I have found that the losi diff fluid isnt the greatest,, seems thinner and doesnt last very long. maybe ofna would get better life.
just a thought
thanks
MO