Thanks Bojan for the detailed feedback. It is good thing that we were able to rescue such a nice piece of optics.
Regarding aperture stops, please note that with camera lenses the iris is an integral part of the optical design and its location is important - especially for wide angle lenses. As Ray suggested, the placement of the aperture stop at the front is only valid for image points that are near the centre of the field. In the corners some of the aberrations sneak back because the aperture stop lo longer lines up with the entrance pupil as defined by the iris set for the same f-stop.
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