I agree. The oem parts are easy to mix up intake and exhaust valve seals. They are the same color and one digit off on part numbers.
Furthermore, if you used supertech seals the colors are unintuitive.
Intake seals are brown
Exhaust seals are blue
Worth checking if you've got the cover off.
Also the valve cover spark plug tube seals certainly go bad over time and allow oil to accumulate on the plugs.
