In my experience the WD40 is good {not great} for getting off sticky nuts, etc., but it has rusted the crap out of things I used in on in the past.
When I was a kid I found WD40, and had a ball with it. I sprayed it on everything even my Marlin 22 rifle, which stayed at my grandparents house. I remember spraying my rifle down with WD one weekend, and comming back the next weekend to find it crusted in rust.
I went back to the old 3in1 that my grandparents had plenty of {which wasn't great, but never did what the WD did}.
Years later, I got a fairly large storage shelf from a local auto parts store that was changing over its brass fittings. I put all of my orphan bolts, and nuts into the plastic containers. I then sprayed them down with WD, a few weeks later I was looking for a bolt and CRAP!!! They were all rusted!
Since then the shelf is still in the same location, and after replacing the rusted bolts, and nuts with new {or, maybe better, not rusted}, and using nothing to lube them I have never had another problem........