@Ralph: Thanks for that find! Will be fixed.
EDIT: Here is the fixed level: http://home.arcor.de/braindamaged/9.mlf
Just put it into the MM folder and overwrite the old level 9.

@Damocles: Thanks. Have you tried to set the mipmapping method to "trilinear" (in the tune panel)? I´ll look into this.
Edit: Yes, the street is a block. Have you a horizontal "seam" at the street or is the texture "grainy"? Then the mipmapping doesn´t work right. It would be good to know if it has something to do with your DirectX settings.