Anyone know what is best to remove the GM factory waxy yellow rust proofing / undercoating ? Thanks in advance.​​​​​​​

 

Pretty sure that's not factory applied.
I've seen a thread or 2 about that stuff, not easy to remove iirc.

 

Dry ice removal maybe?

 

I found degreaser and a paint brush works best but its time consuming and messy, not something you can do in the driveway.

 

For what it's worth, there are places that steam clean engine bays. IDK if that will take it off or not.

 

ive used mineral spirits to clean the bottom of my vert before I re-undercoated it with fresh undercoating. it didnt hurt the factory paint but took the undercoating off. you could try a test area and see if that works

 

I removed mine many years ago with a gel based engine degreaser from Gunk. I sprayed it on, let it sit and then pressure washed it off. It was messy and a lot of work, but it came out looking really good. I did need to do additional detailing after removal to clean up any residue, but for car shows, it was worth the effort to me.

 

Have you tried using WD40 it works really well.