I am getting a chuckle out of all of the regular WD-40 talk. An in-law of mine from Houston worked for Pennzoil. Pennzoil supplies the raw products to WD-40, or at least did at the time. They also made the exact same formula labeled "PZ-1" Pennzoil.
He told me that WD-40 is 95% Kerosene. Yep, plain old Kerosene. Smell WD-40 and go smell some Kerosene. Smell familiar?
That said, oil products and water don't mix, so water displacing it does well. That said, there is no "magic" in there.
I tend to keep that in mind when I apply it somewhere. Ask yourself, "If I am using WD-40 to protect my bore from rust, would I use Kerosene in the same spot?" I have even seen people recommend that "magic" WD-40 can be used to wipe down kids' high-chair trays. YIKES!
BTW, of course it will ruin a stock finish. Why would someone wipe it on there? It is not a wood protectant, and I don't think it claims to be. Would you wipe Kerosene on a stock finish??
Hope this keep things in perspective. Best wishes, and God Bless, Marc