Penetrant test

I have used Kroil, PB Blaster and regular WD-40 with really good results, however if I run into a bolt that is really stuck, I just plan to hit it with multiple applications of the penetrant usually over a day or so.
I have found it to be the exception when a stuck nut - bolt is positioned so the bolt threads act like a funnel.
A good video, I like it that this guy gets to the point without a bunch of: Bright lead in Graphics, Wild Music and excess BS about the importance of his show.