What size is the p/s o-ring?
 

I can't find a dealership who knows what size o-ring goes in the pump, and all they sell is the entire assembly. I know somebody posted it here before but I did a search and came up empty. I guess I could take mine out and phyisically match it up at an auto store but I'd like the dimensions just in case.. it's hard to eyeball one that'd be 1-2mm off.

The O-ring part number is 062610110 and costs about a buck

You can find the diagram HERE It is part #19

Personally, I would not have too much confidence in a dealer who:
Couldn't find this part, or
could find it, but would rather tell you you had to have the whole assembly.

.

According to this "how-to":

http://www.subaru-svx.net/photos/files/How-To/14304.pdf

The o-ring is 11 ID x 15 mm OD (7/16" ID x 19/32" OD). Kind of an odd ball size. I went with a 7/16" ID by 5/8" OD o-ring. Seems to be working fine so far. Get a viton o-ring if you can. Stands up better to temperature and oil than nitrile or buna-n rubber.

That should work. It isn't all that exact and other small size differences should work fine. :)

Great thanks for the help :)

Since you have to take the reservoir off anyway you can just take that with you when going looking for an o-ring.

Get a few spares in case you have to change it again.