If your vehicle is showing oil pooling in the spark plug wells, here are the most likely causes and the parts you'll need to fix each one.
The rubber seals that isolate the spark plug wells from the oil-filled cylinder head harden, shrink, and crack over time due to constant engine heat. This is the most frequent reason for oil leaking into the wells.
If the valve cover was recently serviced, the tube seals may have been pinched, rolled out of their grooves, or installed without the necessary dab of RTV sealant at the mating joints.
A blocked PCV valve causes excessive pressure to build up inside the engine crankcase. This pressure looks for the weakest point to escape, often forcing oil past otherwise healthy spark plug tube seals.
Over-tightening the valve cover bolts during maintenance can stress and crack the plastic or aluminum cover near the spark plug tubes, allowing oil to seep directly into the wells.