Sounds like you're talking about the front oil seal, which IS pressed into that hole in the timing cover. Here's a few pics I took from a Haynes repair manual for you. Don't worry if the photos look different than your cover, these are for a V8 engine. They didn't have the same photos for the /6. The first shows how you can drive out the old seal with a punch from the front of the cover. Be careful not to bend the thin edges of the timing cover itself. The second shows how to use a special tool to drive the new seal back into the cover. I just used a small block of wood to protect the seal and drove it back in. The third shows installation of a micro sleeve to repair the wear groove on the hub at the back of your vibration damper (harmonic balancer). I originally thought the groove was there for the seal to "pop" into, until I read this manual. As strange as it sounds, the groove was worn into the metal by the rubber seal.
Make sure you spread a thin layer of sealer inside the micro sleeve first. It makes it easier to slide on and also ensures proper sealing of the groove. TAKE YOUR TIME AND TAP ON SLOWLY. Use a block of wood here also. This sucker is very thin and will bend easily.The front seal and micro sleeve should both come with instructions.
Hope this helps,
Jerry