I plan to use the suggestion someone else posted here of slipping a piece
of PVC pipe over one of the cylinders, the right length to slip over the
shaft and wedge against the cylinder in the full-open position.

Not quite as elegant as replacement cylinders, admittedly, but a lot
cheaper and (from the sound of it) probably longer lasting.

             _ _
  __ _ _   _| | |  | David M. Brodbeck (N8SRE)              Ypsilanti, MI
 / _` | | | | | |  +-----------------------------------------------------
| (_| | |_| | | | @ cyberspace.org
 \__, |\__,_|_|_| "To the optimist, the glass is half full.  To the
 |___/             pessimist, the glass is half empty.  To the engineer,
                   the glass is twice as big as it needs to be."