About 20 years ago I used to think WD-40 was the best thing since sliced bread, because it brought my wife's recalcitrant Citroens (Dyane and 2CV) to life on a damp morning when she was on early shift, enabling me to go back indoors and have a nice cup of tea. The alternative was using the supplied starting handle for around 10 minutes, maybe with the aid of a hair dryer.   

But what they don't tell you is that WD-40 then attracts filthy gloop all over the plugs, coil etc and after a while makes the problem worse. Eventually I discovered NGK plugs which made grazed knuckles and bruised wrists a thing of the past.

Oh sorry, friends in the States - maybe I ought to explain that said "cars" were designed by the thrifty French after WWII, utilising left over Junkers 52s for bodywork and flat twin air-cooled concrete mixer engines!