In my R&D gearbox i use Mobilube LHC LS.
http://www.autokreso.hr/ulja/downloa...S%2075W-90.pdf
Might tryout Castrol SAF-XJ since i have it lying around.
http://www.ge39.com/files/SAF_XO_SAF_XJ_B1174_96.pdf
Both are LS, limited slip which you cant use in a synchro gearbox, "to slippery".