I second twiggy02919’s comments. Anytime I disconnect a plug, I always put a dab of di-electric grease in there. It doesnt take much, just enough to cover the connection points. My brand of choice is CRC’s Di-Electric grease (http://www.amazon.com/CRC-05105-Technician–Electric-Compound/dp/B000CIRU6W/ref=sr_1_1?ie=UTF8&qid=1314706793&sr=8-1)
I have used the same can for over 6 years, and I use it when re-seating sparkplug boots all the way down to when I replace bulbs.One note, it is not entirely necessary to use this grease on plugs that are in your cabin area, the grease is generally for areas that have exposure to the outside elements (rain, mud and in my case, cats that crawl up under my hood and pee on everything).