The subject of what to use for rusted on bolt removal has come up at times on this board and generally the use of a 50/50 solution of acetone and automatic transmission fluid is usually favored. This month in my issue of Airheads magazine for BMW motorcycle owner's there was a short article on this subject.
Machinist's Workshop magazine tested penetrants for breakout torque on a controlled "scientifically rusted" nut. No details on the size of the sample, but trusting they used something appropriate, the results were as follows:
No oil 516 lbs
WD-40 238 lbs
PB Blaster 214 lbs
Liquid Wrench 127 lbs
Kano Kroil 106 lbs
ATF-Acetone mix 53 lbs
Kind of interesting to have some data confirming an accepted opinion.