I have been watching this thread with the yea's and nay's on WD-40, and thought I would throw in my two cents.
I am on the side that says no WD-40.
Why? Because it does leave a varnish base if allowed to dry and gells when puddled.
When I attended Colorado School of Trades / Gunsmithing. You were given one warning NOT to use WD-40. If you were found with it after that you got a two day suspension that had to be made up before graduation.
Anyone doubting this please call the school at 1-800-234-4594 and ask for Mr.John Stewart, the Chief Instructor. Tell him Russ Baker, a former Honor Graduate, sent you.
I have heard that Trinidad was a bit more harsh with a two week suspension. I don't know that to be a fact, but I do know that formal training in gunsmithing, at most accrediated schools, prohibits it use on firearms.
While I was working as a full-time gunsmith at the Firearms Service Center in Lakewood, Colorado, I had the opportunity to examine hundreds of rifles that were "lacquered shut" from the use of WD-40...To the point they no longer functioned properly. This Laquer, or Varnish, is not something you can easily see, but requires a complete DCOA (disassemble, clean, oil, assemble) to have the firearm function properly again. Prior to attending CST, I did all this (DCOA) and thought it was me that was performing the miracles, because the gun worked fine after I did my magic and put it back together "correctly".... I didn't have sense enough to know, because you can't see the varnish, what the real problem was.
Remember, it only takes a few .0001 to maximize tolerances on a firearm, and a light coat of residual varnish can do just that.
Now, having said all this, do I still use WD-40? Yes, Sir!
But, I have learned to not over use it, and to wipe throughly after using it. It is at it's best when used for what it was designed for...Water Displacement, formula #40! NOT a lubricant, NOT a fish attractant, NOT for Hemorrhoids, NOT a chrome polisher, and NOT a cleaner, albeit it does a fair job at about all of this....just remove it after using it.
Those who use it, and believe in it, without taking proper precaution to prevent build-up, you Sir, are looking for heartaches somewhere down the road.
Just my thoughts on this age old discussion. (I think it's as bad, or worse, than the .270 vs 30-06 discussion). Perhaps it's a healthy thing, and that's as it should be. We make our decisions, and we live with our choices, no matter what! And I like that.
Respectfully, Russ