It always seems like its the last bolt to a project that decides it doesnt want to loosen up. We have all been there; most likely using a breaker/cheater bar and eventually snapping said bolt causing even more grief. A good rule of thumb I always tell people I do work for is to pre-soak any bolt I will be putting a wrench to quite often for about a week. A good penetrating oil like “PB Blaster” works wonders; along with other quality brands. HEAT is also important and makes a night and day difference especially with leaf spring and shackle bolts. The bolt itself likes to sieze right to the rubber bushings and fight you every step of the way. Most people dont have access to a set of torches, but a good and cheaper alternative is a benzo torch which can be picked up at most hardware/auto stores. It does not burn as hot as a set of oxy/ace torches but will still help get the job done. Always wear the appropriate protection as bolts will stay hot long after they have been heated, also falling chunks of rust can cause pretty bad burns too. I usually like to use a breaker bar with the top section of a jack handle ( insert the breaker bar into the top of the handle so it wont wallow out the section that combines with the bottom handle attached to the jack) This way you can gradually increase pressure as oppposed to an air tool which can cause bolts to snap and or bolt heads to strip with a sudden increase in torque.