What's the technical problem??
"Problems" can sometimes be cured by replacing the "o"ring on the outlet from the pump. (34439FG000)
Have you tried changing the fluid as a first off ?? (Done by using a large syringe to empty/fill the reservoir, circulate fluid, emtpy/fill reservoir again, etc., until the fluid looks fresh)
Pump part number for the WRX is 34430FG000 superceded by 34430FG0009L
Same pump fitted to 2008-9 Forester XT