I want to clarify that there's no law against using WD-40. Certainly professionals who know how to use it correctly on a sewing machine and, more importantly, know how to remove it completely before oiling, can go ahead and use it. Here is both a recommendation and a caution about WD-40 and vintage sewing machines:
http://www.treadleon.net/sewingmachi...gmachines.html
Most of the people on the QB are not professional sewing machine repair people, however, and would not be able to correctly remove all of the WD-40 from a sewing machine's innards. If the WD-40 is left in there, it will gum up the machine. Here is a thread that mentions what happens when you do not remove WD-40 from the inside of a sewing machine:
http://sewing.patternreview.com/Sewi...ns/topic/84285
I would also caution anyone who uses WD-40 for any reason to use it only in an area with excellent ventilation -- preferably outside (although I could still smell it on our chairs that were kept outside, even months later).