It sounds like you are talking about the high pressure line. Unless you are sure that is where the leak is, I would try replacing the return line first, just because it is really cheap and easy to do, and a it is a common point of failure, so it certainly won't hurt to replace it even if it isn't leaking yet. If that doesn't solve your problem, then move on to the more expensive fix.
Subaruparts.com PS diagram
I'm talking about part 4. I think you're talking about part 16. Ouch.
