WD40 through spark plug hole???

[40 Deluxe]

Don't waste your time nor money on WD-40. "WD" = "Water Displacement", 40th attempt to get it workable. If you have water condensation or droplets on a surface, WD40 will break the surface tension and let the water drain off, is all it does. It's not made to be a lubricant nor protectant. Read the labels of various products at your local parts store. Something like PB Blaster Lubricant (not Penetrant) may work.