Large O ring on dizzy? Rubber or other

Standard black O-rings are termed "nitrile" or "Buna-N". It resists oil, but not gasoline. Turns hard over time with enough heat. AC type are HBNR and come in various colors (grn, red, blu) though trying to standardize on green. They are tougher and handle heat better and I think are better than nitrile for most all applications. Viton are usually dark brown. They resist gasoline and last longer than nitrile. They cost more and are hard to find in larger sizes. Harbor Freight sells kits for each type (english & metric for nitrile). Your life will be easier if you buy each kit.