I suppose the idea of resistance makes sense.
The flash circuit (in a Mamiya RB Seiko shutter at least) is inside the shutter housing, along with the X/M switch. There's a set of physical contacts that are triggered as part of the shutter action. It's all a bit steampunk-mechanical compared to modern engineering. So corrosion or oil/environmental factors could gunk it up.
That said, I can't believe all six of my lenses have exactly the same condition
especially since their shutter blades are clean and functional, and since my 180 got a complete strip-down and the entire shutter got a solvent bath in white gas yet still won't fire a newer (and el cheapo) radio trigger..
I'll have to assume that the RB lens synch circuit just has more resistance than a smaller vintage shutter (like my various RFs and Nikons from the 60's/70's) or a modern SLR/DSLR. I can't recall how the X/M synch works either, but I'd guess it has to choose at which point the shutter is considered "open enough for flash" and that this makes the circuit more complex.
As I understand it, a lot of the build up of resistance is due to arcing or other consequences of high trigger voltage flash circuits.
A lot of RB67 were used in studios with high power studio lights. Many of the older studio lights used trigger circuits that involved high voltages and appreciable currents. As an example, I have an old Bowens Monolight location kit where the trigger voltage is 600+ volts, and I am guessing that the current isn't miniscule.
The modern cameras - including many film cameras - use electronic switches. They just get fried by the high trigger voltage flashes.
Older, smaller film cameras were probably not used as much with high power studio lights.
