Hello Bravlin,

it's always difficult to reconstruct things that results of strech operations or organic shapes from subd operations, but that's the right place to discuss such things.
My proposal:
get 4 profile curves and 2 rails
join the segments and rebuilt them with a tolerance of the treshold 0.005 units
make the sweep

get a curve for a railrevolve from the original also and rebuilt it
create a railrevolve axis perpendicular to the curves end/center
create a isocurve on the railrevolve and trim there
build a G2-Blend between the trimmed railrevolve and the sweep

Hope it helps!

Have a nice weekend
Karsten