I've just replaced my sparks with Denso Iridiums,and noticed one of the coil packs was filthy (the one nearest the battery). Its got a rust coloured coating from the bottom to about half way up - it rubs off ok,but it's also inside. It seemed to be done up as tight as the others. The others look like new! Any ideas - could it be on its way out? No misfires or anything.