Won't be head gasket, this would have totally different symptoms!

If there is oil down the plug bores then you would have to of spilt LOADS of oil for that to happen! No point in cleaning plugs, easier and cheap enough to buy new, in fact far better to buy a complete service kit, and do your service at the same time! Plus this won't cause the hunting, they do suffer from misfires and the culprit will be the coil pack, assuming the rest of the ignition system is in good condition.

Martin