Hello,
The impeller for the 3JH5E engine has the Yanmar reference 129670-42531. The lid of the water pump uses an o-ring with Yanmar reference X0506590-01.
Sometimes the original impeller comes with the o-ring. I keep one o-ring in the boat. Some impellers have an inner thread so that a special tool/screw is needed to remove the impeller as referenced to in the engine manual. I also have this small tool on board.
Osculati has the equivalent part 16.194.05 which I have used ultimately. It has not the thread and I use a pliers to remove it. Sometimes the piece is destroyed when removing. So, if it looks OK on inspection I will not remove it.
Regards, Luis