From many years of freeing rusted bolts, I found that you don't heat the bolt, you heat the area around it. If you heat the the discs, the same thing happens, they expand in the hole.
Mostly, I would agree with this but I just avoid applying torches to receivers and would not advise anyone to do so just not knowing how far they might take it. Heating the bushing will of course temporarily expand it in the female threads. But they will not expand at the same rate and this little differential expansion is often enough to break the bond or allow the penetrating oil to creep in. Then, upon cooling, the bond may be broken.
I have also unstuck many frozen rusty bolts by heating them dull red and allowing them to cool rather than heating the machine or part they are threaded into. Very often this allows the bolt to be removed without any penetrating oil, and it minimizes any risk of heat damage to surrounding areas.
Kroil is not my favorite penetrating oil. It was about all we had while I worked for GM, and I saw it fail to penetrate more than a couple threads deep on many occasions, even with prolonged soaking. The remaining threads would be as dry as a popcorn fart. And these fasteners were seldom severely corroded. To me, the claims that it would creep into spaces as small as a millionth of an inch were marketing hype.
