Hi Stefan - so as far as the geometry goes the problem seems to be these collapsed slit-like openings here:






Those have 2 vertical planes attached to them, with the planes stacked up right on top of each other, overlapping the same exact space. At one point did you possibly have 2 lines in those spots duplicated right on top of each other and then joined to each other? It looks like something like that anyway.

That kind of hole that has opposite sides touching each other is a type of degenerate trimming boundary and so they will need to be removed - the way I'd try to remove them would be to delete the vertical planes and then do an "untrim" operation on the slit boundaries to remove them. There is some information on untrim here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4

I'll see if I can clean this up for you by doing that.

- Michael