I recall it was 75W-80 but now it looks like it's advertised as 75W-75? Did the formulation change since then?
https://www.bgprod.com/catalog/driveline/bg-syncro-shift-ii/
> BG Syncro Shift® II is an API GL-4 gear lubricant blended to SAE 75W-75 viscosity and may be effectively used in all vehicles where engine oil, ATF, or GL-4 gear oil is specified as “service fill” for manual transmissions.
https://www.bgprod.com/catalog/driveline/bg-syncro-shift-ii/
> BG Syncro Shift® II is an API GL-4 gear lubricant blended to SAE 75W-75 viscosity and may be effectively used in all vehicles where engine oil, ATF, or GL-4 gear oil is specified as “service fill” for manual transmissions.