The new style RCA sockets were a recent change, the old ones used white insulating washers for both the left and right RCA sockets, vs the new style that have colour coded washers. Sounds like the manual makes reference to the original style.
I agree the new style sockets are much higher quality, i binned all my originals long ago and replaced them with these Rean sockets so thumbs up to Bottlehead for doing the same.