I have painted PVC on windows, cause when I have gone in to decorate, I have found the previous colour all over the PVC, or they have gone too far to be cleaned, as the dirt has been there for so long and cause I coulnt get it off, I would paint the PVC, with the customers consent of course.
I havent had any comeback yet, and have done this a few times.
The best thing to do is undercoat the PVC first, then apply a satinwood or eggshell finish, both in oil-base, I think gloss is too glarey, but a satinwood finish still has a sheen too it, but not in your face like gloss.