I have a solution that has worked for me so far; I cleaned up as much of the deterioration as I could and then applied Sugru, slowly building up the missing knob. I used a covid mask to create a slight texture effect (meh). It has been stable for nearly a year. You might give that a try.
I also use Chemical Guys VRP on almost all plastic surfaces, it has oils that rejuvenate the ABS plastics and looks great. You might also give that a try. I've stopped using Armorall.