I think I have exactly the same leak...mine is on the driver's side. Crawled under the car, couldn't see anything at first, then noticed an oil drop up by the back of the engine...probably the valve cover.OK, so this is now resolved. The part is called a "cam plug" and there are two of them on the back of left-bank valve cover. My leak was on the larger one (about 2.5" in diameter) that's behind the intake camshaft. There is also a smaller one (about 1" in diameter) behind the exhaust camshaft. Both of them together were $14 retail. I went ahead and replaced both. The guy at the parts counter told me it is a very common problem, and the symptoms are exactly what I had with it being very hard to find the source of the leak.
From above, I can't seem to figure out how to get the engine cover off. The front section is easy enough but the back part must have some hidden clamps or something! How did you do it?
Also, was replacing the grommet (cam plug) easy enough? i.e. is it simply a screw off-screw on process?
THANKS for any help you can give me!!!