The other leaky o-ring on the power steering pump
 

FYI

The o-ring on the fitting that goes into the pump (the high pressure side, I believe) is 7.5mm ID and 1.5mm cross section (10.5mm OD). It appears to be viton and should be viton from everything I have read. Viton has the best chemical resistance and high temperature peformance. It can handle synthetic oils due to it being a fluoropolymer. Viton seems to be the material of choice for most hydraulic applications. Most of the hydraulic viton o-rings I have found online are 75A Shore Durometer.

I tried to use some HNBR o-rings I had in a kit but it didn't hold. They were too soft (70 Shore) and I don't think they liked the synthetic oil. They also weren't exactly the right size. The closest size in the kit is an english size which has a slightly larger ID and OD. It got crushed on the outer diameter by the fitting. These o-rings are great for low temperature applications like the A/C fittings but not this application.

I couldn't find a lot of posts about this o-ring so I am posting this for posterity. This o-ring is Subaru part number 31260GA050.

Now, can someone tell me the suggested torque when tightening this fitting? It isn't clear exactly how this fitting seals when tightened. Best I can tell, the bubble flare at the end of the line pushes outward when tightened which causes the o-ring to squeeze between the line and the nut.