The c33 does not have interchangeable view screens (...at least mine doesn't) - - it is assembled very much like the c220 is, with the fresnel and the ground glass as described by Steve Smith. The Fresnel is actually glued to the ground glass in the corners
That's as I remember it. It is however, easy to take apart by an amateur 'repairman' so it may have been assembled wrong in the past.
Leave the screen alone on a C33 unless it needs attention and you enjoy resetting the spacers.
If you have two bodies, two lens pairs, and one lens pair does not focus correctly on either body, then that lens pair is out. The viewing lens is sometimes shimmed between the barrel and the lensboard for this adjustment. You actually adjust the focal length doing this as you alter the front and rear element spacing, but it is normally good enough. If the unwary try to unscrew the lens front cell they sometimes loosen the barrel instead, and the shims fall out. It does vary with the lens, but most have a retaining ring on the back that loosens with a lens wrench which is easiest to work on.
There is just a chance that the lensboard is bent, but it would not seat well. If the body tests well with another lens, I'd assume the body is square.