Was using D2X-XL, sorry (Understand I haven't been in the Descent loop for sometime).
The other version being just running the descent2.exe, assuming D2X-XL didn't overwrite any files to skew the results.
D2X-XL revealed the seam more noticably than regular Descent 2, but it's still there in both versions. Probably differs by the resolution. The second texture is causing it and I don't know how to fix it *shrug*.
A copy of the map can by obtained here if you have the time to take a look at it.
That's entirely up to you.