Just chiming in again, as I finally repainted some my interior vinyl parts yesterday and so far, the results look promising. Used up a can of SEM Landau Black which was enough to cover front and rear door panels, glove box lid and steering wheel pad. Still need to repaint the sun visors, armrests and dash pads.
My interior was originally dark green, door panels were two-tone dark/light green.
I prepped the parts with several washes with dish detergent, scotch-brite scrubbing and a thorough wash with a semi-nasty vinyl cleaner. Had to clean some parts several times, as the 40+ year-old gunk refused to budge without heavy persuasion. Then, I sprayed on a tack coat first and went on with a few covering coats wet on wet, as the vendor over here recommended. Parts look nice, color looks even and seems to sit firmly. SEM is good stuff.