very little oil may be ok. I had pools of oil in a couple of my plug holes so a new valve cover gasket was a must. I also had about 170k+ miles at the time.None that I could tell. VERY small amount of oil in one or two of the spark plug chambers, and a bit on the plug threads on the same, but we're talking eyedropper-type amounts. Still a potential issue?
Edit: Forgot to mention, all of the plugs looked good. Standard wear and discoloration, no oil residue, and no oil on the insulator or above.