Oil around outside of spark plugs for #5 and #7 for 00' 5.3

[ZBrink]

Please see the below photo. This is a 2000 5.3. I noticed I have oil around the outside of two spark plugs for cylinders #5 and #7. The engine is running fine and I don't seem to have consumption.

Is this a known issue? What could the causes be? I don't see any oil leaking from the bottom of the valve cover gaskets.

Thanks in advance!