neutral bar is burnt
Replace this panel before it burns your house down!

You need a new panel not a new neutral bar, as this panel is trying to cook you, your kids, and your house as I speak.  The FPE Stab-Loks are rife with trouble, and as you have seen, will attempt to burn your house down instead of doing their job.  In particular, at least one of your breakers is out of calibration i.e. not tripping on a low-level overload that should have eventually tripped it, and the excess current is slow-cooking your neutral bar, and who-knows-what-else in the house.  Also, that slow-cooked neutral bar isn't making good contact with at least one of the neutral wires, which is what is causing the voltage imbalance in your house, most likely.

Until then, keep your smoke detectors working and your fire escape plans practiced, as it's not a matter of if, but when this panel will ignite again...