Penetrating oil first, let it soak for some time. Then, if you can reach the head of said bolts, rap on them with a hammer (in a straight down motion, and a side-to-side motion) for several minutes. The vibration, together with the penetrant, may help loosen the mechanical bond. Good luck.Kroil Oil or PB mentioned above.
FIRST... apply Liquid Wrench (or a similar penetrating oil). Let set a bit (1/2 hr minimum).
Use an impact wrench if possible, if not, use a heavy box-end wrench on the bolt (preferably the nut if one exists) with hammer blows applied to other end of said wrench. This creates your own "impact" tool.
Just make sure you hammer it in the right direction.
My two cents & experience.
Enter your email address to join: