Could be your centre diff / viscous coupling. Running on a flat is effectively the same as running on a tire of the wrong diameter. This is really hard on the viscous coupling in the subaru AWD.
Change your transmission fluid. If it comes out sickly black and slippery like silicone, you've pooched the coupling.
Change your transmission fluid. If it comes out sickly black and slippery like silicone, you've pooched the coupling.