Opposed aircraft engines are notorious for leaking at the center of the case halves. Subaru's typicaly don't, but here's a rather amusing fix that due to regulatory reasons I can't say I've actually seen it done. (But it does work...)

 

First loosen the two bolt on either side of the leak. THOROUGHLY clean the area with mek or laquer thinner.

Plug the valve cover pcv outlets and duct tape your shop vac hose to the oil filler.

Turn on the vac and apply Loctite 515 or Threebond 1104(Yamabond). Press sealant in a little and turn off the vac.

Allow 12 hour or so cure and don't tell the FAA you did it.

That sounds like it's applicable to Harley-Davidson and VW engines as well. I'll have to remember this one.

I think the Subie community is a little less strict than the FAA, which i could certainly see as being an issue at 15,000 feet. however that fix sounds really neat and tricky/sneaky which makes it even more fun.