Yesterday, I turned the heater blower knob to max only to see smoke rising from the wooden loudspeaker grille and a distinct smell of burning plastic (while my Triumph used to catch fire behind the dashboard quite often, I didn't expect this in a German car). I switched if off and removed the knob by turning the bezel holding it in place, feeling behind the dash, it seemed okay, but since putting it back together, I can't seem to turn the knob as far as before (it used to turn easily, then give a click before reaching max). It also doesn't blow as much air as before, but at least it doesn't catch fire anymore. I checked the fuses and they are all fine, should I just leave it as it is or replace it? And how difficult is it to replace?