Ditto on kennyd's analysis.
My main use for WD-40 is to spray it on oil drips on my concrete on driveway apron. Too many visitors cars' leave an oil drip or two. A squirt of WD and rinse off with water takes good care and doesn't leave a stain.
A little-known product called Blue Creeper is the best (IMO) for penetrating rust and getting into tight places. Much improved over Kroil products, but likely will never make the big time. It's a "go to" oiler for precision oiling like sewing machines, and a miracle worker if rusted bolt threads.