What is this?? Spots on cab corners

Anyone know what this could be? I thought rust spots, but the cab corners seem to be plastic caps.

I noticed it last night on the passenger side as I was cleaning off tire shine sling. Then this morning I looked and it was on the other side as well. Is it the tire shine ruining the plastic pieces? I used a product for the first time on Friday. I had black dots all over the truck from tire sling but these didn’t come off. I’ve tried clay bar, compound, and an iron remover. No dice.

Any...

What is this?? Spots on cab corners