You shouldn't be using wd40 anywhere on a car and really not any of the places you've mentioned.
I've said it many times that I was an idiot to use it as I did...true story! Honestly! But, in this one application, I got away with it.
There was a very authoritative post from a guy that had credibility to me...forget who or when, but he said that there is almost always something better for the car than wd40. On plastic to make it shine...it may, indeed work, but long term there are issues with what you're doing to the plastic...if you really put it on the paint...eeeks...on the engine itself...it's flammable, you know...eeeks.
I actually wrote a post about looking for a non-flammable lubricant, and there is one...didn't get it, but I know there's at least one. It's funny, though...I went to maybe 7 places (HD, Lowes, Hardware stores, auto stores) looking for non-flammable stuff...I found flammable, extremely flammable, and explosive lubricants, so ironically, wd40, only being flammable, somehow seemed pretty safe! LOL
So, the point is, I'm not endorsing wd40 for use anywhere on the car...though I did use it on the sap, and I have used it also in my door locks. That's it.