Check both valve covers and possibly the timing cover.
Don't forget that the spark plug orings can leak too.

I would pay special attention to the mating surface for the valve cover where the timing cover meets the heads. This is sometimes uneven.

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black