Hi, my favorite helper for these things is a 1/4 inch wide cold chisel, 
about 3" long. This size is thin/sharp enough to cut into a rusted 12 mm nut 
without having to bludgeon the thing to death. Hold it with vice grips and 
hammer it into the nut so that it is trying to loosen the nut at the same 
time. If the nut loosens, good, if not you'll split it open in dozen modest 
whacks. A true 'nut-cracker' is much nicer, gentler, but won't usually fit! 
Don't beat adjacent components into submission, chain reactions get 
expensive.  tim s.

BTW Excellent sig! is it copyrighted? are we holding a sig 'bake-off', lock 
in your votes now viewers..