A GL-4 or GL-5 gear oil is required by Torsen Type 1 units. This oil provides high-pressure additives needed to prevent the oil from breaking down under the extreme conditions generated by the tooth mesh. A 75W-90 is recommended, but higher or lower viscosities can be used if they meet GL-4 or GL-5 specification. Either synthetic or conventional oils can be used as well.
I seem to remember some production vehicle that came with a torsen and they kept exploding..hopefully thats fixed. Good luck with yours.