Hi Brian,
I have the 6Hp Tohatsu engine, I only use it for about three weeks peer year so I did not replace the impeller. After four years it let me down. I have only myself to blame, I am very pleased with the Tohatsu in all other respects.
I had it replaced when in for service, so not actually done it my self, but I would recommend it is done each year as Tohatsu suggest.
Regards
Graham Ebb
Blue Jazz 235/25