I don't know about the earlier models, but the AD headlight switch is darn near indestructible. A 12v system will draw half of the current as an equivalent 6v system, which helps longevity. The only place I've seen problems with these is the dimmer rheostat - the coil can be broken, but it seems to be a rare problem.
My dad's '51 had a terrible headlight problem - they wouldn't turn on, would flicker if they did, etc. I replaced the original headlight switch with another original that I'd rehabbed, and all is well. The '51's switch looked solid, so now it's in the rebuild pile.
Pry apart a complete used original, polish all the contacts, apply your electrical grease of choice, and reassemble. Ready for another 50 years of trouble-free service. They're built far heavier than the generic replacement switches.
