Paul, a couple of mine are loose too, and I don't know how to fix the problem. At point of manufacture the rings would have been a slip on fit over the two handle halves then shrunk in a roller press. I imagine the press would have consisted of three rollers with one being able to exert the pressure required to shrink the ring into the groove.
I used to think about the looseness of the handles, and how to fix them, a few years ago but I've got used to using the braces as is.
Now the problem is at the front of my mind again!
Cheers,
Geoff.