Dear Paul, your comments are music to my ears, I pride myself in detecting flair in lenses when shooting advertising shots as an assistant with Chris Maguire in London, Bow street studios. If this is the only problem with the lens then it is not a problem.
With regards to preference of the C lenses, it is felt that these are of beautiful design, all of them! I prefere them over the straight conformative design of the more recent lenses.
When we purchased a new 503 some years ago and bought all new kit, I was dissapointed with the lens designs and wondered why they had been changed.
The new lenses all have a flaw, the sync chord area has a plastic mount which snaps off if you forget to push the cable release button. Expensive item to replace and despite Carl Zeiss sending us a complimentary one, we have not put it on the camera because it is prone to do it again.
The older lenses do not have the plastic casing and are more robust. There is argument that the cable would come off these too easily but we never found that to happen. You could slightly squeeze the flash sync cord to give it more grip, never a problem and it would come off the lens quicker if someone tripped on it.
I am in constant search for these older lenses in mint condition, I just love the retro look and when on the camera it reminds me why I purchased a Hasselblad all those years ago. Why pay more for a lens if it is doing the same job. Beautiful, keep the new lenses I don't want them! I prefere to take pictures with stylish equipment, best wishes, Carl