I have my old motor sitting in my garage and have decided to freshen it up a bit. I've gotten the valve covers and intake manifold off and I noticed that the passenger side rockers are all oily clean (the oil has burned nicely over time). On the driver side though the rockers are all covered in a scaly flaky oil residue. It's not wet oil but burnt smelling and easily flakes off when you scrape it. Why is this like that?

 

pretty good sign that head, or at least those rockers have been removed or replaced at some point.