strange coolant leak

[exdrocca]

I've recently noticed a coolant leak from my passenger side valve cover. It's a subtle drip from the valve cover that puddles up along the intake manifold towards the front of the engine. I don't know how long this has been going on but i was down about a half gallon of coolant. I did check the oil, and it's clean and normal as can be. How else could there be an external leak in that area that's not getting into the oil? This is for a 350

Thank you