I just did the same. Used carby cleaner. Give is a spray, leave it for a min or two (while you spray otehr areas), get one of those dish brushes with a scraper bit on the end, or make your own plastic scraper. Scrap off all the understicker off (will still be super sticky). It will build up on the scraper, peal it off and chuck it... Then when youve got most of it off, giv it another hit of carby cleaner and move to the next. Work around all the areas. Come back to the start, give it another quick hit and then get a cloth to rub it all off, if you missed any bits with the scraper get into it again.
I didnt have any problems with the sheen on my plastics, but be careful not to let puddles of the stuff form as it may soften the plastic too much. And Carby cleaner is pretty aggresive shit so try wear some gloves and keep it off ur skin. Also do a little test area first to see if its going to stuff your plastics.