If this O-RING is degrading and going soft(or hardening off depending on climate and conditions), or just worn out through wear and tear, the problems of leakage is probably a problem best avoided!
For all our other spares and consumables, why not browse the Products Gallery and schematic for your model, it may help you specify a more complete order, taking best advantage of the shipping charges.
Check the schematic for your model (where available) and take a better informed decision when placing your order. No company is more pro-active in seeking out those rare Japanese NOS spares!