On Friday, April 6, 2018 at 4:55:52 PM UTC-7, wrote:
I dont use the docking rings anynore, after a few years they deteriorate to mush. I now use a short length
of silicon tube that fits over the instrument tube, a much better lasting material, and cheap.
Dave

Silicone is a good choice. If you prefer O-rings, though you cannot always go by color, green ones are used in auto air conditioning system seals and indicate HNBR. This would be a particularly good rubber for glider tubing "clamps" as well. See the link for HNBR characteristics:

http://www.mantaline.com/capabilitie...e/hnbr-rubber/

bumper