Good to see you are wed to the Ortofon Sound, I share in this same attraction.
I have a few MM's in storage and do intend on bringing them out for a play time, as I have not heard them with my latest Phonostage.
The MM Cart' AT 20ss you refer to is one I will investigate and learn more about it.
The Replicant 100, Paratrace and Fritz Gyger FG 'S' are all sharing the same form as a Styli, the 100 is seemingly being separated from these other forms not only by name but also by suggesting the 100 has undergone a ulterior polishing treatment.
The Dimensions for the Three Styli are the same and the only variances are the name used for the Styli, the dimension tolerances found in the patent for the form of the Styli, might only be the other difference, maybe?, one Brand offers a very tight tolerance for the dimension used across the supplied styli, but this is not known to me or have I seen this discussed as a potential possibility or as a fact.
'needlestein' is a Cart' rebuild Service in the USA, who makes their work available to seen, the evidence and customer feedback will show the service offered is quite capable to take on the work if a FG 'S' is on the wish list to be used.