Is this little body piece in front of the rear wheel a factory option or is this aftermarket . Unless it significantly helps with aerodynamics, I'm thinking about removing them because they are getting cracked up.

 

Pretty certain those are factory, they were on my 88 gtu as well. I have a perfect book with an image that suggests that they came on series fours

 

They aren't supposed to be painted, just black plastic. They were part of the s4 aero package.

 

I think they are cool, repaint and keep

 

The stock pieces are made out of a rubber-ish material and are black. It's the same material the factory duck bill spoiler is made out of. I would suspect that the material is not paint suitable as it is squishy to the firm poke and tears (like high density foam would) rather than cracks. You can get splits or tears in the material. They are part of the S4 areo package and coupled with the duckbill spoiler, spats in front of the front wheels, thin trim piece under the front bumper, and aluminum tray under the engine lead to the lowest CD FC produced by Mazda from the factory.