Think something has been sat on the seat for a time, should come out with some time in the sun ??
It is the rectangular finish and ours is the half moon, the Half moon has the least stitching of all the options and is the most water ingress resistant, in addition it has slightly more lower back support.
I can only imagine the owner is trading his ST and the seat won't add any value to the dealer so it's being sold separately......if the dealer only knew what he had like we do !!

Who ever pics it up and IF it suits their shape/weight/height will be very happy.......it's the single best farkle on ours, 830k's the other afternoon with only a 15 minute fuel/food stop riding 2 up.

Cheers