вот, наткнулся на инфо на буржуйском форуме - долго мусолили и пришли к:
I agree DON'T DO IT for extended periods of time. It is for emergency and diognostic use only, not to get better gas mileage.
It doesn't actually make the car FWD but forces the clutch packs to give maximum torque to the front axle. Most subarus today would see ~80% of the power at the front wheels. You can spin the front tires with this but it still puts some power to the rear. Additionally, I understand that you will likely burn up the Duty C solenoid which is big $$ to replace.
Keep in mind, if Subaru felt it was a good way to improve mileage they would sure as hell advertise it and sell it as an added feature.
extreeski & spread eagle are totally correct. And if you blow your differential, don't whine when they don't cover your powertrain warranty. People abusing warranties is why we all suffer the struggle to get legitament warranty work done.
Put a transmission oil temp guage on and watch, it will rise due to this mod.