Thanks all for the helpful feedback!
I agree, the diameters are off which is the root cause.
As I recall, due to unusual bike tubing diameters chosen for extra strength, standard seatposts did not fit well.
Builder machined a slip collar from aluminum stock which has a top collar 1/8" high that got powder coated to the steel frame. Not sure I want to remove it to make a thicker collar.
I looked at my torque ratchet and we are not tightening to 15nm, maybe 10 to 11 or 7 to 9 foot pounds. Not that much really.
Also, we used Framesaver product in all the steel frame sections and had product running out for a while, which lubricated the seatpost if the bike was laid down.
I drilled a tiny hole in the dust cap inside the S&S couplers so as to be able to blow compressed air through and push out/ dry out the framesaver.
I carefully clean and wipe the downtube and seatpost every so often but have not seen wet product for quite some time.