If you are pulling the valve cover I don't know why you wouldn't take the opportunity to check valve clearances while you are in there. It's free and gives added peace of mind (unless you find something amiss....)
Oil can be like blood from a head cut. A little goes a LONG way :oops:
With all the engine bay airflow the oil could be originating from anywhere and blown back by the fan. Is the fan oil stained?
Get underneath and check for telltale drips. Sump, oil pump cover, front main seal, oil level...