Im new to rc cars but was wondering if the diff on the HPI firestorm is really sealed? When I pulled it apart there was no gasket or anything. It says on the HPI site that you can run oil in the diff. Also Im using 7000 wt, how much do I put in there? Do I fill up one side or both before I put it back together? Thanks guys.

Are you talking about the diff cup or the gear box? If you put diff oil in it you should only put it in the diff cup where the spider gears are. Fill it up to a little over the cross pin.

Sorry Im new to this, what is the diff cup? I have the gear box pulled apart, and I see big drive gear. Is this what I pull apart and apply oil too? SHould I lube any other gears when I put it back together? Thanks