Mark, would I steer you wrong!
I did this refinishing a year ago & it looks
just as fresh as the day I painted it.

Get the spray product designed for the job!
There are may to choose from.
Not expensive.

The trick is to FOLLOW the directions.
Be sure to read the can & buy the recommended
solvent/cleaner to prep the surface.

Any good auto paint shop/detailing shop
will have the right stuff.
Find someone who looks like they know something
& tell them what you want to do.
Lots of people are buying these products.
You want the one designed to adhere to plastic
& vinyl & is made to "flex" with your bumper,
dashboard, etc.

I removed my front grilles & windscoops,
cleaned them,
prepped the surface with solvent, let it dry,
then applied two coats of this special satin black
spray paint, allowing to dry between coats.

I had everything back on the car in four hours.
***Of course, without this list I would have been
at it a lot longer--I found the grille's "fasteners"
mysterious
and irksome.  I found them illogical.

Good luck with your project,
Phaedra
'85  Wolfs Westy