There is something called "adhesion promoter" for plastics, I will not pretend to be a paint expert but I believe you will find it worth 5 minutes of your time reading about it if you are wondering if plastic needs any special primer.
I'd also "scuff" the plastic prior to applying the primer or adhesion promoter with sandpaper, maybe 100 grit? to improve the mechanical bonding of the first coating. I think if you can get the base layer to adhere properly, the color coat will be fine.
Adhesion promoter! Thank you. I couldn't for the life of me, remember what it was called.
Yup, the adhesion promoter did the trick. If I squint, the mirror cover almost looks factory. Basque red is hard to match. Gotta give a lot of credit to body guys. It's not easy to get paint to look good.