[SeaCay]

The o-ring specified is 37.5mm x 2.5mm and can be found online at numerous places, such as: https://tameson.com/sealing-adhesives-and-lubricants/sealing/o-ring/general-purpose/30-to-100-mm/nbr-o-ring-37p5-x-2p5-mm-70-shore-a-25-pcs.html