I am a complete idiot. Finally went out to fit door seals bought (at a very friendly price) from gatos in his recent sell-off of parts, only to find that the V40 and S40 seals are different (it's because the top part of the S40 rear door curves down slightly before the corner, whereas the V40 goes straight on). I'd never noticed this and had assumed that they were interchangeable.
So: I have rear right-hand door seals from a phase 2 S40 if anyone's interested. Specifically the one that's on the car body, going round from the the B pillar all the way over the top to the back of the bottom sill, and the main one that fits on the door itself, going all the way round - they're numbers 4 and 13 on the picture here (click on pic to make it a visible size):
http://www.swedishautoparts.com/S40/...-moldings.html
(link also helpfully located by gatos - thanks.)
I paid I think £15 for these so just looking to get that back if possible.