Cary SLP-98 history and iterations

I've been looking into the SLP-98, possibly thinking about buying a new or used one. I've been doing some research and, while I can see that there are many different iterations of the preamp going back twenty years or so, I find it difficult to determine the differences. I'm hoping someone can explain at least the last 5-10 years of production.

Specifically: a number of comments out here refer to the F1, which seems to be the upgraded version for the last decade or so. But the current model on the Cary website doesn't list the F1 option (though it lists many upgrades); further a couple threads out here seem to suggest that the F1 came in at least two different versions. If I were looking at used models, is there one to look for? (And what did Kevin at Upscale have to do with any of this?)

I am also curious about whether there's consensus on which iteration of the preamp is the best within the last 5-10 years. If it's only a matter of difference, depending on subjective taste, that's one thing, but it does seem that the F1 is considered better in years past. I've also read that the current/new model is more transparent, less "syrupy," which many seem to prefer--but what do I know?

Thanks!