I use diff oil in my 1/8-scale racers but the MT does not have a seal but I guess you could use some sealer. Oil makes the diff act like a limited slip diff and depending on how heavy the oil is you can adjust the how much slip you have. Instead of using oil I use HPI spring kit on my MT. I tried to find a link to the springs but I am getting ready to leave for a race but I know it is on HPI web site.