I like to soak manifold bolts with a name brand penetrating oil of some sort for a couple of days then take a 3/8 drive impact and lightly squeeze the trigger and use that "hammering" action to help break the bolts free. If you can't control the amount of pressure on the trigger you can adjust the regulator on your compressor down. I started using this method years ago after breaking a couple bolts in half because I couldn't tell if I was turning or twisting the bolts while using a breaker bar.