I had the passenger side intake cam plug leaking, plus the valve covers leaking. I just got done with the resealing, take a look here:
http://www.subaru-svx.net/forum/showthread.php?t=48682
Like Paul said, it's probably the main seals, cam seals, or valve covers. If it's the oil pan, it should be pretty easy to see, and best of all, that's one of the easier ones to replace since you don't have to take the engine half apart to get to it!