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To get to the shifter shaft seal you will need to remove the gear shift lever and the left (stator) side cover. This can be done without draining the oil by laying the bike over on its right side. Be careful about leaking gas and/or battery acid if you do it this way.
Note how the wires from the side cover are routed and be careful not to pinch these wires when re-installing the side cover. You may also want to get a new gasket since you are likely to tear yours removing the side cover.