I'd put my money on an axle, probably the moist one. Did you check to make sure the grease boots on the axles weren't torn or compromised? I doubt it's the diff. On the other hand, it seems like you'd know that:

http://www.peachparts.com/shopforum/showthread.php?t=270477

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition