The pair on the Liberty are: 1.5mm CS X 2.5mm ID 90D NBRI suspect the Avenger is the same and can measure your spares to verify. OD would be 5.5 mm.70D would b easier to install, but will wear out sooner. If you can find polyurethane, last longer than NBR. PS: Avenger schematics show two: Cal 5.5mm O ringφ2.5*φ1.5 hardness 90° JSR
Here you go:https://www.oringsandmore.com/buna-90-o-rings-2-5-x-1-5mm-minimum-25-pcs/https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=368_52_1002&products_id=41763[/quoteThanks Robert
Here you go:https://www.oringsandmore.com/buna-90-o-rings-2-5-x-1-5mm-minimum-25-pcs/https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=368_52_1002&products_id=41763