Oil in the spark plug wells can be as simple as careless / messy oil top ups.
I know certainly on my Abarth from where the filler cap sits if I miss and slosh a bit around the engine cover it'll drain down into the rocker cover and into the spark plug wells in with the coil packs.
This is particularly exacerbated by the Abarth's thirst for oil requiring regular top ups too!
You'll know for yourself if you've been topping up with oil wit any regularity or if you've topped it up recently this could be your issue. Likewise if it's been serviced recently that could be it.
Your other option is to look at the rocker cover gasket. If the gasket has failed it is more than capable of leaking into the spark wells. Typically of course people only tend to notice it when it starts to leak outwards round the edges of the cylinder head as this will then drip onto something hot and smell or it'll leave a black mess that's obvious to see.
If you're going to change the rocker cover gasket make sure you remove all of the old one, any burnt or stuck on bits, clean the surfaces, use a bit of instant gasket to stick the new rubber gasket in place and then fit the new gasket and replace the rocker cover. The last thing you want is for the new gasket to move or worse still pinch and tear, leaking again immediately.