It's inside the door, attached by two screws on the side with the latch and one 10mm bolt on the door face (after the door panel and plastic sheet is taken off).
see part #2 on this page:
http://www.subaruparts.com/diag/?mod...category=602-A
I don't think there are any sources just for the motor assembly, you have to buy the whole thing. The plus side is that no re-keying is required as that's a separate part. To replace the part, you have to take off the panel, remove part of the plastic sheeting, remove the screws and bolt, unhook a couple of rods and two electrical connectors, pull it out, reverse to install new. I'd guess about a half hour job, only need a large phillips head screwdriver (for two screws mentioned), medium phillips (for door panel), 10mm wrench, a little dexterity wouldn't hurt either.