Ten small O Rings. These are Nitrile Rubber (NBR) and according to wikipedia are good for temperatures from −40 to 108 °C. Wikipedia also says resistant to oil, fuel, and other chemicals.

No extra postage for additional o rings (this one or others I am selling). Posted in a plain envelope (usually a first day cover and not parcel post if indicated by eBay). If you want to pick up from Bethania that is fine (and no postage cost).  I normally post withing 1 working day of receiving your order, Australia Post does experience delivery delays, so reach out to me if not received on time. I do not provide a registered or express service but can add a priority stamp if you pay the extra $1.20.