[lry99eldo]

I've found that not all rusted fateners can be treated to remove. When the two metal surfaces get corroded together in such a way heat is the only way to get them to release a bit in order for the penetrant to work it's way into interfering with the bond. Depending on how much time you have, access to the fastener, and so on, I'll heat two surfaces as equally as possible several times. Expansion/contraction IS MOVEMENT, that's what frees up corrosive welds. Just as the metal is cool enough to apply the penetrant I'll soak it, and then repeat as much as 4 or 5 times. I'll then test it first tightening it just to stress the surface tension and the loosen to see if it breaks free. This usually works.
Then there is the drilling method. Starting with the smallest bit I can and working up to as close to the minor diameter of the bolt/stud as I can. It weakens the structural part of the fastener. That's depending on all other factors too, location, time, tools and place, and so on.
And as some have mentioned, theres always the acceteline wrench, but if possible I'll grind the head off smooth, remove the unit being held in place, and then work on the remaining fastener to loosen it hopefully saving the internal threads. If it's a through bolt and access to both ends, blow that sucker off and punch it through.
If all else fails, Heli-Coils are cheap!
lry99eldo