Single stage paint job.. no shine

Didn't they use to make a 30% clear with SS? It isn't supposed to shine. The only thing it think could be done is...a very light 600 grit and SS clear. But, if you don't know the brand, you will probably have adhesion issues. Metallic will flatten and look like dirt in the paint. I know there are a couple professional painters here and maybe one will reply. I'm not and painted a few. I would try 3m machine polish, purple bottle, light not aggressive. My 2cents. Ask the previous owner who what when. Craig