Tubing makers have manufacturing tolerances. When you put a caliper on a pile of seat tubes, those tolerances are quite evident. Factor in heat distortion which is especially evident in brass brazed lugs and this explains the different sizes of seat posts.
I think it was JBZ's Tesch that had a slipping seat post. Tesch was/is a great builder but there's a good chance that the seat lug was brass brazed. There's nothing wrong with that but at brass brazing temps the seat tube will distort. The better the brazer the less it will but regardless it will distort some. When solid binder ears collapse against each other generally this points to the seat tube ID isn't round and/or the seat post isn't sized correctly to the frame. I think JBZ's fix is a good one but I'd measure that seat tube ID. If it isn't round or at least close, slipping might start up again.
Curt Goodrich
Minneapolis, MN