I have imported it in Magics, and it's giving errors. i tried to repair it, but even magics isn't able to repair it directly.
I did a shrinkwrap of 0.5mm, now it hasn't any errors anymore, but the dimensions are slightly changed.
It's attached, so you can check if it's giving the same kind of errors.
Can't you check it in the modeller why it isn't manifold?
Bart