The difference between Contax-AE and Contax-MM lenses is actually just a small nose on the outside of the lens bayonet. This nose presses down a small lever on the outside of the camera's bayonet. When this happens, the camera recognizes an MM lens. You can also press this lever by hand, and then you can see that the camera allows Tv, for example, as a selection option and uses it. The thing is: this also works in the image results! Good AE lenses (especially the prime lenses) actually also function as MM lenses when the small lever is moved! According to Zeiss, MM lenses additionally have smoother aperture mechanisms so that the aperture automation always works reliably; using an AE lens as an MM can therefore cause problems. I would bet less on the — of course — threatened defects, but rather on underexposure due to imprecisely closing apertures. After all, I've also noticed that my Tokina 17mm sometimes reports incorrect aperture values (9.5 and 13) to the camera via the aperture simulator in the upper apertures 11 and always in 16. That's just the disadvantage of mechanical transmissions — they need to be absolutely precise. But if you have no scruples, you can try using your AE lens as an MM and let me know if everything went smoothly.