I've used Dupli-color CP199 Clear Adhesion Promoter Primer with excellent results. I found it in the auto parts stores and I believe it was available on your favorite internet mail order sites.
It comes in a spray can . I spray a little in a small metal container and apply with a swab.
It softens the surface ofplastic and leaves a CLEAR primer surface. I never had any type of plastic that it didn't work on in auto ,motorcycle and household projects.
Read instructions on the can for best results.