I think the knobs are made of some sort of plastic that your oils from your hands degrades after a while. My hands, which seem fine on everything else I've ever owned, destroyed the "tire tread" that went around the main tuning knob on my Yaesu FRG8800 in about 6 months. Yaesu gave me a free knob, but yanking off the old one was a tremdously big deal. The service tech told me the knob just pulls off, but after the front panel started to flex, I ended up dremeling it in half with a cutter wheel. And I destroyed the rubber on the new one within a year or so. I had a video card in my PC years ago with defective fan blades that fell off as time went by. Eventually, the card overheated and there were only about 2 blades on each fan hub. They knew about it and sent me a new, better card under warranty. The fans glowed under UV light, but apparently UV light rotted them out.