take a paper towel, fold it up into a square, then wipe under the valve coves lip. it could leaking v/c gaskets.
if they are dry, clean the puddle up, then spray it all down with brake cleaner, then watch it closely to see where its coming from over the next day or so.
when you mop the puddle up try to see if its a mix or just oil, its hard to tell in the pics what it is.
and is it just that one bolt valley with a puddle?