Nate,
Wow... depending on what engine you have in your Eclipse (1.8L SOHC, 2.0L DOHC, or 2.0L DOHC Turbo), you could be looking into a messy job. The 2.0L DOHC (with or without turbo) engine is known as an "interference" engine. Sound bad... well it is. To take off the valve cover and replace the gaskets can involve removing most the belts. This includes the timing belt. Screw up your timing on a 2.0L engine, and you might as well buy a new car.

Seepage out of the valve cover is common. To fix it, get yourself a new valve cover gasket, and carefully replace it. Note: DO NOT OVERTIGHTEN THE VALVE COVER SCREWS! Your valve cover will crack, and they are not cheap to replace.

Torque for the valve cover bolts is only 2-3 ft.-lbs. If you're not sure how much this is, use a low-torque (in.-lb.) torque wrench.

If you were to replace the valve cover gasket, you shouldn't need to replace any other engine components. You can always use additional gasket sealant for additional reliability. I would suggest having any belts replaced that seem worn at the same time... Timing belt, A/C, power steering, and water pump belts. A torque wrench is an excellent tool to have; whether doing this job or any other.

Now, that was the bad news. If I understand it, you are noticing oil accumulating near your spark plug wells. Well, if that is correct, your problem may a very simple fix. I had the same problem last year. Simply replacing the oil cap fixed my problem. You can buy one from the Mitsubishi dealership for $8. The reason why it was leaking was because after time that rubber gasket on the oil cap gets hard and fails to provide a good seal. When the oil pressure and heat builds up, it leaks past the oil cap and seeps under the spark plug cover. You could even just replace the oil cap gasket for about $2.

Good luck stopping that oil leak!
Anthony