It was funny how my original degraded, not linearly. It looked good until two years ago, then the black coating started peeling off, then last summer when it got hot outdoors, they turned very shiny/gooey, unlike any summer prior.
I'd never cleaned it with anything more than mild detergent solution, and can't even recall using the cruise control buttons in the last decade or so. They appear to be silicone rubber so probably not a good idea to put armor-all/etc silicone on them.
I did have a bulb burn out and replaced it with an LED (hard soldered on not a "bulb" retrofit) around 5 years ago. The new aftermarket ones like I linked (probably Donalds' too) are LED rather than incandescent, didn't notice much difference in light output but a little less uniform than the original.
I've only had mine installed since summer, looks good still but no idea how long they'll hold up.