Hi Rudy, looks like a couple of things were just slightly off on your initial curves:



Zooming in on the area marked #1 above, the profile from the side view is not actually aligned to the world axis, it is slightly off to the side from it:



But actually the bigger problem is the area marked #2 above - the rail path curve is not closed, it is an open curve that has its ends crossing over each other, kind of like an X at the end instead of it being closed:



That causes the resulting object to not be a solid, instead it is a non-closed surface that has some part of it intersecting itself, that is probably what is making the booleans work strangely in that area.

Hope this helps,

- Michael