Great fix! I'd be interested to know how many miles the car had covered? Also, how much was the coil? Did you take the plug(s) out in the end? Did you get any error codes logged? I think I might smear some silicone grease on the rubber gasket on ours to try and prevent this. I found something a bit similar on a Nissan, where a dealer had pressure-washed the engine (not a coil-on-plug engine) and half-filled the plug cavity. I found it before it caused any problems,