I had a 99 CR 250 that had black plastic on it. When it was time to send her to a new home(2008), I cleaned her up really good and though she'd been stored inside, the black plastic looked a little dull. I used Formula 2001 car polish, Formula 2001 Protectant and a wool sock.
Put the protectant on first, let dry and then buff with the wool sock. Repeat with the creamy car polish, then one more coat with the protectant. It shined like a new penny. Didn't cost anything because I had both products on-hand. I repeated the process on my son's KX 65 with the same result.
Tank