I thought someone had mentioned an LED "work around".
The back lit, translucent switches on these amps are drop dead gorgeous as is the anodized, high quality casework on these Yamaha products.
There was also a class A integrated amp, the A1 (?) as I recall but more rare than the others.
My understanding is that the original switches used a normal incandescent bulb, which was then wrapped in a colored, rubber (?) cover to give them their one of a kind beauty......but I may be wrong.
In any case, given the growing list of fans and no shortage of the C4 and M4, perhaps someone will sell a repair kit.....