Great! Glad to hear that you solved the problem! At $35-$40 for the two knobs, they were definitely worth replacing.
It seems that some of these newer type of plastics get sticky over time. Some of the higher end cars such as Lamborghini, Ferrari, Maserati have the same problem with interior trim pieces. People have been complaining, and replacing these parts is much too expensive. For items like that, there is one company called Sticky No More which refinishes the parts. I've never used them and I'm not sure how good they are.......However, they seem to have good reviews.
Sticky No More - Exotic Cars Interior Refinishing Services