This sort of thing bothers me.
I recently cracked the case on a console radio to be met with a musty wave of air and chalky white controls in similar condition. Internet searches for "plastic mold", "chalky white film knob" and similar are largely useless. Though after wading a bit I found this thread:
Which offers up some solutions to the problem. I think I'll avoid the dishwasher one, as, if this is indeed a byproduct of early plastic decomposition I doubt I'll want it anywhere near my food. Just a quick share, mainly secure the thread without another half hour of aimless searching for myself (while avoiding the creation of yet another topic specific forum bookmark in my browser).