WD40 is a brand with multiple products now, think they own plus gas now and gt85.
The best used to be automatic gear fluid, the red stuff (50%), mixed with paraffin (25) and diesel (25%) if using red or 28 second burn heating oil you need to drop 5% and add more Auro fluid
Hence the other release agent. As I have found that penetrating fluid is the wrong term
At a guess you have seen the wd40 motorbike disc brake photo.