See several docs in the How-To area, here:
How-To Documents >> Steering System
If you're thinking about rebuilding your pump, let me know. I just did this, and the guide posted there doesn't mention a few steps and tools you really need.
Also see the diagrams on SubaruParts.com:
Power Steering System
also
Oil Pump (exploded diagram of P/S pump itself)
(you'll need to create an account and be logged in for the above links to work).
There's just one O-ring between the tank and the pump. No O-rings or seals for the two bolts that go through the tank. This is the most likely spot to be leaking, and is very easy to replace. Good first thing to try.
The second O-ring the dealer mentioned could be the one at the tip of the high-pressure hose, where it presses into the compression fitting on the side of the P/S pump (on Steering System diagram, reference 34930B, P/N 31260GA050).
I suspected I also had a leak where the low-pressure hose attaches to the tank, so I also replaced the hose clamp there.
Inside the pump are five O-rings, a gasket, and a seal around the shaft.