Had the same problem Im almost certain that your valve cover(tan) front bolts are loose. The head is made of aluminum which can lose its threading with steel bolts easily. Check your valve cover by looking at the bolts. take off the valve cover and replace the rubber gasket and add proper amount of gasket seal(Ultra blue by permatex is good) and remember to scrap off the old seal carefully with something like a credit card. Now for the stripped holes youll have to get a longer bolt but same material(steel) and size and have a nut underneath and tighten to the proper torque which I forgot but you can find it in the service manual.
http://www.zeroyon.com/index/content/view/24/47
As for the middle bolt if it has a stripped hole= I havent tried it but you can use a helicoil or go 1 size bigger. After I did those steps their where no more leaking. And one more important thing= when you bolt down the valve cover you need to bolt it a different way= angle bolting but you should read the manual for that. I hope that helps. Good luck