Hi John,
If something is moving in the spectrograph, you should see this in the lamp spectrum ie calibrating the lamp spectrum using an earlier lamp spectrum should show an error. The spring in the core module is there to hold the collimator lens in position, To hold the grism in position, the allen head grub screws should have been retightened after adjusting to make the lines perpendicular to the dispersion direction.
Cheers
Robin