Opposed Forces is good, but almost always has Parts shown in the diagram which are not listed below in the table. Which is annoying, because you think you've finally found the Part you're after, only to have it not list the Part#.
Try Subaru FAST II. It is the official Subaru Parts Catalogue software, where you can enter a VIN and it gives you the details incl Part#s and Paint Code etc for that vehicle. I have the catalogue file up to 2012 incl all non-JDM/USDM cars like ours (all models, not just Legacy/Liberty). But there are catalogue files downloadable online for all JDM and USDM models too. You have to download it (not as easy as going to a website), but well worth it
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Or just let me know what you're after, and I'll punch it in. It can also search by model instead of VIN (like Opposed Forces) , but I find it easier to use a VIN if available.
EDIT: And yeah, like others have said, the Workshop Manual is what tells you how to service it, but doesn't list any part#s.