There is a seal in the timing gear cover. It can easily be replaced, sometime by not even removing the timing gear cover.
There is sometimes a groove worn by the seal into the surface it rides on. There are a
variety of repair "sleeves" being sold to eliminate the leaks. I like the complete kit sold by Rockauto - seal, stainless-steel repair sleeve, and sleeve installer (no need for glue/adhesive for this style repair sleeve).
