Thanks kkarmical, my order to the O-Ring store with shipping was $9 and some change, and I have enough o-rings just using their minimums to rebuild my rifle at least 4 or 5 times over. Here is the direct link to the Yellow forum post that contains direct links to the O-Ring store:http://www.network54.com/Forum/581291/thread/1302911529/Marauder+.177+and+.22+O-ring+list
I would say Buna-N and Viton are equally good for high pressure air, except for O-rings subject to abrasion (breech or bolt O-rings). For that, Buna-N generally has better abrasion resistance.