I had the same issue and had the reusable valve cover gaskets with the steel core. Did you use gasket sealer on the gaskets? I didn't and when I did the leak is now gone.
I used regular rubber valve cover gaskets that came with the felpro (I believe) rebuild kit
when I did it the first time I did not use any sealer/rtv or anything
I had to trim back the locator tabs on the gaskets a bit to clear the aluminum covers and I'm wondering if the gasket just did not stay put
so I pulled them off, RTVed them I'm place and tried again
it if still leaks tomorrow I will pull the intake bolts and install the thread sealer
I should have some left from when I did the water pump and timing belt housing