Thanks for your reply. I think I would want to be able to inspect all the bearings and CV couplings along the drive shaft to the tail rotor.
Take your point about wing spars, but corrosion is a slow process, amply covered during C and D checks, and the wing spars do not have moving parts requiring lubrication because they do not rotate during flight! The couplings and bearings driving a tail rotor do, and can potentially break up quickly. I think I would want to check there was no visual evidence of bearing or joint stress, given how critical the tail rotor seems to be.
Twin tail rotors would simply be two shafts running down the tail boom, each driving a tail rotor, so there would be one rotor on each side of the tail boom instead of just one on one side.