The other day Grace carried a handful of crayons in her chubby little hands out to the car...and left them under her car seat. A couple of days later, a heat wave made the car an instant oven, and when I went to remove the car seat, I found the melted mess underneath.
This was about halfway through the clean-up.
Vastly improved, but still visible when I finally called it quits.
Another solution that someone mentioned was placing a dry towel over the spots and running a hot iron over top. I didn't try this method, but it certainly would be something to consider. You wouldn't have the fumes from the WD-40, but I wonder just how much would be absorbed, as there would be no way to draw the wax into the towel, except by blotting.