From the factory the trans & diff use 80-90w gear oil , now there are synthetics that work better , make sure you use a sythetic gear oil designed for manual trans as the regular synthetic gear oil is too slippery for the syncros to work properly. The easiest way to tell if the diff is a sure grip is too jack up the diff & spin 1 wheel , if the other wheel turns the opposite direction it is not a sure grip, if it turns the same direction with the trans in neutral or won`t turn with the trans in gear it`s a sure grip
