I have always (never failed) with this method.

Soak with PBlaster, let sit for about 2 hours.
Put large wrench on nut
Cover any area that can be damaged with a folded towel
Smack large wrench with a mini sledge

One good whack is all it has ever taken.

__________________
Current Bimmer
2004 X5 4.4i Sterling Grey Sport/Premium

Past Bimmers
1991 318I Alpine White
1995 740I Alpine White
1991 525I Schwartz
1998 323IS Scwartz
2004 330CI Cabrio Titanium Silver Metallic
1995 540I Schwartz
2000 Z4 3.0 Titanium Silver
2000 330ci Coupe Titanium Silver