In most cases it doesn’t require a lot of heat to help out. It just needs a temperature differential. I find that if I leave something in my unheated garage in winter and use a heat gun in the morning on the outer parts then the difference in temperature between the large parts, which remain cold, and the heated flange or nut is often enough. I sometimes freeze tools such as drifts or even entire assemblies if they fit and only heat the outer part.
The other thing is that some of these parts can be locked with thread sealant. The heat from a heat gun is more than sufficient to soften most sealants.
We also have CRC penetrant in a can, not the standard stuff but the product specifically marketed as a penetrant. It’s especially good on rusted on bolts. I’m in the habit of spraying the stuff on every day for a few days and leaving it to work it’s way in.
I also use shock and even a rattle gun on occasion, it really depends upon the composition of the components.
