external oil leak at the head gasket

I would replace both head gaskets. Get quotes but it will probably run around 2 grand. Make sure they include a new timing belt and resurfacing the heads.

Getting closer.... Bob, leave this one alone please. KGPW: USUALLY the right head OIL leak is preceded by COOLANT seepage on the left head...but not always. If your RIGHT side is not actively losing coolant, then try thickening the viscosity of your oil to 20w50 for southern climes or 10w40 for wintry ones. If the leak doesn't abate, and/or you're losing coolant anyway, BOTH HGs should be replaced, as the motor's coming out, the t-belt is being removed, and the head(s) should be shipped out to a good machine shop for planing and pressure testing. Total time for the house wrench is about 10hrs for a careful generalist, 8 hours for an Subie-experienced pro. Figure $1.4-1.6k total inc the new head gasket kit, machine sublet, with t-belt, its idler and tensioner pulleys. Be extremely careful to torque the NEW head bolts correctly, and do NOT ignore the machinist sublet (even though Subaru dealers sometimes do when squeezed by skimpy warranty labor timing. Your '07 F is 13 winters old. Think about whether you want to plunk $1.5k+ into this old chariot...especially if it's looking at new brakes and tires coming up. May be a tricky call. The 4EAT tranny acting ok? Be sure to change its ATF too. Good luck, and best holidays all. Ern TSG/B

I'll give Bob credit for suggesting that the leak may be a cheap, innocuous one from the vc covers, but KGBW5 was specific re HG seam leaks...perhaps evidenced by inspecting said seams underneath the motor. But if perchance it's just vc spark plug gasket washers I'd swap the wet plugs for new iridiums, clean the boots, and swap to a thicker oil with a bottle of seal conditioner...saves pulling the VCs off.

You have a point Ernie. If this were my car I would try to live with it rather than spend the money that could go towards a newer car.