I think just about anyone with over 100k on the car has had to experience this.
Most likely cam seals and crank seal.
Crank seal is easy to replace and at the same time I'd recommend doing the timing belt since you have to just about take it off to do it.
Cam seals I have not done yet simply because you need a special tool to hold the sprockets in place to get the bolt loose, but once off they should be no harder than the crank seal to replace.
If you remove the radiator it makes the job alot easier with the extra room. It can be done without removing it but then you run the risk of punching a hole in it with the back end of your mechanics pick if you have a stubborn crank seal.
There is a good how to on doing the timing belts that will get you almost all the way through the crank seal job.
http://www.ryanmacdonald.com/car/howto/belt/belt.html
Also check these threads
http://www.subaru-svx.net/forum/show...threadid=18266
http://www.subaru-svx.net/forum/show...threadid=18200
http://www.subaru-svx.net/forum/show...threadid=18287