I very much doubt this, since Sturmey-Archer hubs don't have plastic seals or nuts. Either you or the person you claim to be quoting are confused.
Just FYI a while back they were bought out by SunRace and just out of curiosity I picked a couple of their 3 speed hubs and did find part number HSL871 which is listed as a plastic sprocket dustcap. Whether that has an effect on the inner fluid I doubt it but don't know for sure and also am not sure if they are using other plastic parts these days. My guess is probably not a whole lot of stuff but it was an interesting find.