rm125 1992 or 3 has water in oil

[fisherman25]

hello my rm125 has water in the oil. Im pretty sure its the water seal behind the impeller. just wondering how I get the propeller of. it has a allen key screw thing in the middle of it. but when you try to turn it the whole thing turns. how do I stop it from turning so I can undo the allen key screw and get to the seal.
any help would be great

[Katman]

The water pump seal is installed inside the clutch housing cover. If you remove the cover you will be able to carefully hold the gear while undoing the impeller bolt.