It appears to be from the leak-off collar exactly as described in Jim's repair guide, so it should be possible to rebuild with Jim's ingenious XM rack gaiter mod. However - I was wondering if anyone out there in Activa-land had a spare known-good rear ram (or indeed a spare known-leaky ram that I could repair and then fit) so that I could dismantle and rebuild the car in one go without leaving it unusable while I repair the leak. I could then repair my original ram and keep that as a spare either for future misfortune or for the next person who needs one...
Of course if someone happens to have one to hand and is going the the X-rally, they may well find themselves with a willing buyer!
