Not too bad, pull the leads out and look down the hole. If you can see oil in there around where the plugs are then it will be the cam cover gasket. If its only a bit damp in there I would leave it, but if it's filling up in there then i'd change it.
Use genuine ford plugs, I've seen a few running faults caused by non genuine plugs, chuck a set of genuine ones in there and it sorts them.....
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