From the looks of the parts manual, it shouldn't be that hard, as it's a single sided seal (as in the seal is only on one side of the bearing).

While your in there, you may want to check the impeller shaft and bearing to make sure they don't need replacement. I know that on the RS250, the impeller shaft needs changing a good amount due to wear from the seal cutting a grove in the metal on the shaft and not allowing a good seal.

When you pull the shaft, you can clean it up real well with some super fine scotch brite and check where the seal sites on it. If it's grooved all that much, you may want to replace it?
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Charles Gallant