If you have a damaged thread and no restorers or taps to hand, you can improvise by cutting a vee notch in the end of a bolt, with a hacksaw. Best to cut out the lead on the thread (where it starts) The bolt will jump the damaged portion allowing the threads to engage further down.
For stuck bolts, heat with a blow torch or similar and cool rapidly with penetrating oil. As it contracts the oil is pulled in. Repeat several times. Try striking the head of the bolt sharply with a hammer to help release the threads. Wire brush the head of the bolt. Apply one good go at moving it with constant steady pressure. If it moves, turn it back the other way and start again, moving a little more each time. If it doesn't move to start with, don't round the bolt off, apply more heat and cooling.
Got me out a few scrapes.
Is this stuff really helping people?
Chris