yes, it's the Kit 100C, so it looks like there are two versions. I suspect when they identified mine as that, they matched up my photo with the old version, but when it was sent to me, I got the newer one, which looks quite different. Mine has no grub screw, but looks like the first picture. Those instructions/diagrams sort of suggest it does just push on, somehow, doesn't it, the one that looks like mine. Not sure how I can get it off if I can't get it to move, though!
Also the photo from amazon of the one with the grub screw doesn't look like the new version I was sent, either. That one has screws through the back, and end-caps on the front. So the amazon photo seems to be something else entirely.
I've asked if they might be able to send me the old version that is closer to mine instead, but I don't know if it'll help if I can't get mine off anyway. And it will rely on convincing them that there are two versions of that part number! I did send links with photos, so it depends who reads the email I guess.
I may have to live with disintegrated rubber I guess, but it seems a shame. It is only an aesthetic problem for now though - although the shower riser twists around easily in the rubber rather than being held in place, it doesn't actually affect anything and the shower stays in position with normal use, so I guess it's fine. Just looks a bit grim!