www.officeworks.com.au/shop/officeworks/p/j-burrows-no-14-rubber-bands-100g-jbrb14100b.

Used on clamshell RDM extensions when the original rubber ring has broken. My rubber band has been in service for more than 5 months, without breaking. Have used the rubbers on Naish, Severene, Simmer and Unifiber RDM extensions and I expect they will fit the North RDM extension, too.

Good quick fix. Not knocking your idea. But, I would prefer to get something more ruggedised for piece of mind. I've had mast clips fail. It's not nice to the mast when they do, and then wonder why sail is not behaving itself during session. Good reminder for me to check mine. Long over due.

veryseal.com/product/34-5x3-55mm-nbr-buna-n-70-duro-o-ring/