Originally Posted by ThunderCactus
WD-40 is not a valid lubricant. Period.
While true, and for people like both you and I, we know this as we learned this in industry. Others have not had that opportunity to learn.
The reason that WD40 is not good for rubber is the Turpentine and Alkanes that make up the vast majority of a can's contents. Both that would aggressively eat away at rubber compounds.
There is a gray line forming now that there are synthetic rubbers designed to withstand solvents and other petroleum products (such as your cars tires). There are still however many applications where even some synthetic rubbers are sensitive to petroleum products. The original poster seems to have lucked out with his rubber seals on his original AEG's.
But penetrating oil, such as WD40 (or some of the better commercial alternatives personally I like Crown's offering but that is purely subjective) have their uses in a shop.
An outright ban of them is silly, especially since most machinists and millwrights I know refuse to use WD-40 and then go and use one of those "Breakaway" agents to undo rusted bolts which is just penetrating oil with a fancy name on the can.