Contax G 90mm problem

I have one of these with a Fotodiox adapter. There is a sticking point in the focussing at about the half way area. I think the problem is in the lens rather than the adapter (same adapter works fine on a 40mm Contax lens). The focus will move beyond this point, but it is very difficult to do so. Movement in both directions is fine until I hit that point. The lens appears otherwise to be immaculate.

Is this likely to be something that can be fixed/adjusted at a good camera technician?
My 40mm lens focuses very smoothly
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Mike Fewster
Adelaide Australia