I would not purchase a C. One of the things that appeals most about the Zeiss T* lenses is the consistency they have, from one lens to another, of their excellent contrast and color.

I like the CT*, because I am used to their aperture and speed coupling and I do not like the CF the way it was changed in that regard. More importantly, I do not like switching from one to another. If, like you, I preferred the CF style lens; I would stay with that, especially if you are going to buy one in less than good condition and have it serviced.

In regard to condition, the reason you buy a lens is for the glass and that should be flawless. If it is not, the price should be deeply discounted. A lens with flawed glass may produce a usable image, but it will not bring a normal price if sold to a knowing buyer. If you buy a lens with glass issues and the price is not reduced, compared to a similar lens with mint glass, you should expect to have to deeply discount the lens if you, later, decide to sell it. Make your seller take that loss, in full. Do not allow him to pass any of it on to you.