im having the same problem. my 04 coupe sat for a couple days, & seen a leak from the center of the car. i hope to get it to my friend, & he can look at it. when i find out, i will keep you all posted.
They just changed the oil, & valve cover gasket on mines.

 

so update on this,

since the last time i seen an minor oil stain in my garage, i took off the under carriage cover on Monday (prob like my 3rd time in past week and a half) I could see very tiny area around the back of my lower oil pan where there is some oil spots. So i started monitoring everyday since last Monday and hoping when oil drops on the floor i can find out exactly where the leak is coming from.

Today is Thursday no oil stains in the garage ( i have been jacking the car up with a jack and looking everyday), i have been driving the car everyday with no under carriage cover (is that safe?)

usually i see an oil stain if the car is parked for more than 2 days.

Even after driving for 1 hour in intense 90+ California weather, i could not see an oil spots.

This is a real mystery that's pissing me off..