You'll need a T70 torx bit.

 

No, he's talking about the rear diff.

I just used a 1/2" drive. It wasn't snug but it worked for me.

 

Dunno if '09 is different, but it worked for me too.

 

1/2" works but the correct size is 13mm.

To get it off you will need to put it up on a ramp to get leverage and use an 18" breaker bar. That *&*&^&*(())*& is on there. I tighten mine up well under the recommended torque.

 

13mm Subaru & Nissan Drain Socket

There are cheaper options, though built around the same idea(socket attachment).

 

I just use a 1/2 inch drive. Works fine for me.

 

The 13mm socket is the way to go. I first tried the 1/2" breaker bar that most people use and nearly rounded off the diff plug. I bought the 13mm socket from Ultimate Tool (a supporting vendor here) and couldn't be happier with it.

 

Would anyone know if the drain plug size is smaller than the fill plug size? For some reason, the square on the lower plug on my 2003 Forester looks smaller than the upper.

 

I wonder if someone drained it before with a 1/2 inch drive and slightly enlarged the opening?

That said, I've always used the 1/2 drive. If it's really tight, I juice it up with PB Power Blaster, and have even used a floor jack under a heavy cheater bar - just slowly jack the cheater up, and let the weight of the car break the tension.

One other tip - if you're not accustomed to doing this service, it's a Very Good Idea to remove the fill plug before the drain plug. If you drain it and then can't get the fill plug out.... well, you can just imagine what creek you'll be up.