My o-rings were ALSO torn after only a few months! Bad design? They should have been well lubed when new. They seem to take some load when installed. Whatever the case, I went down to the local hardware store with the ones that remained and purchased some spares.

They appear to serve the purpose of keeping dirt and grit out of the main bearing area and now that I think about it are probably the reason I had some grime in there, along with not reinstalling my dust boots. And you mention they take some load when clamped down so that's probably the case. I reinstalled the dust boots when I reinstalled them so hopefully the problem is solved.