Dear Brian Chesters,  I had one of these to repair, a couple of
years ago.  I used a condom to replace the bellows rubber but found it
difficult to seal the ends and maintain the correct tension.  Someone
before me had used a contact adhesive which needed cleaning off the
sealing rings, and then I used wire ties to clamp and seal the rubber
in place.  It took several attempts and much cursing before I was
successful.

Being relatively modern, I suspect that someone may have a stock of
spares somewhere which would make life easier.  In the meantime, buy
at least a six-pack!

Regards
Michael Start
London

 [ A six-pack of _what_ ?!  ;)  -- Robbie