Being an actual mechanic for a living, both Dave and Ryk could be correct. I have seen brake lines so tight (chemically married) the only way to get them apart is cut the line and use a 6 point socket to break it loose. A good line wrench definately improves your chances. Only way PB Blaster or WD40 or the like will improve your chances is if it's rusted.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!