I know the feeling Rich
If you have some way of getting some decent amount of heat on the nut. I have often found it usefull to heat the nut up as much as possible. Cherry Red is nice, bright red even better. Need'nt be the whole nut, part of it at a decent temp will do the trick.
Once hot. Quench the nut in cold water........this will often loosen even the worst of heavilly corroded stubborn nuts.
Obvously, take care not damage the thread or immerse the alternator itself into the water
