Richard, I have been meaning to do the same for several years now and not got round to it. I had wondered if the next size bolt might do the trick but have not looked carefully enough. Unless you have much more serious wear than I have, I estimated that a sleeve would have to be very thin ... and made of what? S/S or Nylon or?
Elsa (no 103) won't come out of the water for a bit .. so, unless someone else comes up with a solution before then, perhaps we can liase later.
Meantime if you come up with any magic solution I would be grateful if you would post it here.
Cheers, Chris.