Our '98 Corolla CE has been experiencing some oil loss/leakage on top of the valve cover and in the spark plug tubes for an unknown period of time. The dealer quoted me for around $200 for the fix, so instead I purchased the valve cover gasket (from Texas Toyota parts website) and a set of NGK spark plugs (from Advance Auto Parts) and did the install myself this morning for about 3 hours. Most of that time was spent cleaning up the oil mess/residue on the valve cover and around the engine bay area. I had to use Simple Green spray, a small wire brush, a water hose and plenty of rags to get the cleaning job done for the valve cover (of course I only used the rags for the engine area to wipe down so as not to distribute any chemicals and what not into the engine).
Anyway, here are the before/after pics of the valve cover and engine. Before:
For those who are curious, the car had around 109,560 miles at the time of repair. The valve cover gasket was totally dried out near the area where the spark plug holes sit, so I had to break it in pieces to remove (no wonder there's leakage issues). I got the gasket for $16 plus shipping, and the spark plugs for $4 each (needed 4 total). So compared to the dealer cost, I saved myself a couple hundred easy, and I know that I did the job right
BTW, this is a very easy job, almost on the same level of difficulty as changing your oil except you don't need to get under the car. The gasket replacement job just involves removing the bolts and hoses around the valve cover, that's that. I strongly recommend that anyone whose Corolla has over 100K miles should take a look at their valve cover and/or pull out the spark plug tubes and see if there's any oil leaking. I believe my gasket has never been replaced once from the factory for 11 years!