Oil on spark plugs

Just changed my spark plugs and found oil on 3 of the 4. The tips of the coil packs and the ceramic ends of the plugs were pretty wet. When I removed the plugs the tips were also covered but I'm thinking this is probably where the collected oil in the spark plug well has run down as I have removed them (I hope so anyway) Presumably if oil was getting to the tips of 3 out of 4 of the plugs this would be fairly catastrophic and the car would be running badly? (which it isn't, no blue smoke or smell of burning oil, or excessive oil consumption)

So I am hoping I just need to replace the valve cover seal and spark plug seal. I have been looking at the below guide which includes replacing the cam tensioner gasket and half moon seal but is this necessary or can they be left, assuming they aren't obviously in need of replacing?

If it's just the valve cover and spark plug seals it looks fairly straight forward but is there anything I should watch out for from people who have done it themselves? Was it fairly straight forward?