Yeah, too tight and you'll warp the camera putting film in.
Maybe it's some kind of subtle wear on the back where the film seats allowing the slide to wallow a bit around the proper position. I couldn't really say much without a close look at the camera myself. Have you held a steel rule across the surfaces to check for flatness or some other technique that may apply? If the channel the darkslide goes into has the sides worn away they might possibly be shimmed back to the proper shape.
Hope you can get it fixed soon, I'm familiar with that frustration with balky gear.