have you had your thermostat replaced lately? to the right of the thermostat cover there is a kinda of grayish streak tht runs vertically. check that out and see where it looks like its coming from. If you did hve the thermostat replaced it may not have been tightened completely and coolant could be leaking from there.
dont get all freaked out. what ever is casuing the stains deosn't seem very bad. I am just hyper anal in my watching for leaks or new spots etc. What i do wheni see something that looks new or that i never noticed before is, I look the area over and see if i can obviously descern where the leak/spot is coming from. If i cant do that than i clean the area up really well and watch for it to reapear. If and when it does reappear it will know be more noticable and easier to trace. again dont worry. I'm a bit of a mechanical hypocondriac, i am always waiting for the shoe to drop and have a problem that is gonna cost me $$$.
by the way if your valve covers are leaking you might wanna check the valve cover breather hoses they can get gunked up and limit the air flow whihc causes pressure build up inside the valve covers which can inturn force more oil leakage. (im not that mechanically smart, i just read that last part here on Dweb)
