As to WD40, it has its place I suppose. I banned the guys from using it in the shop as it was misused, in a maintenance shop I find it attracts/holds dust and isn't a good lubricant for what we do.
Because its not a lubricant, its a water displacer which it does very well. I use it when cleaning my bp guns after a water bath. My dad used it for a lube on his guns for years. I got them after he died and they weren't gummy or varnished like so many claim. They were just dry.