Page 11-13 in the manual states oil specs
It says 5W-30 or 5W-40 for temps below -30 to temps above 30
It also says 10W-30 or10-40 for temps -20 to 40 & above.
The manual also states that you can use any brand of oil as long as they are the same API classification & SAE viscosity as those recommended by Subaru. It also has to be energy conserving.
Rotella T6 meets all these requirements(5w-40,API-SM) except one,energy conserving.