Another thought
It occurred to me that if mine simply wore out (I'll wave my Avo at it and see what happens), at what point did others go awol other than by water ingress.
Mine's done around 25k (2004 model - I was out of the country for 3 years then couldn't ride it for a year after that).
Incidentally, it comes apart easily - I didn't have to break into it. There's a further O-ring (exactly like the one on the outside) inside, which appeared to have been effective in mine. However, I sealed the new one with silicon before fitting.