Still working on a friends bike, i realized that the water pump assembly was not working properly. After disassembly i saw that the bearing of the impeller shaft was.. let's say it was "in there"... mostly...
According to the service manual the impeller shaft is an integral part with the bearing. There is a procedure for removing the shaft that is pointless since you cannot actually buy the shaft it's self since it comes as a single part with the entire right engine cover!!!
Fortunately there is a standard bearing size (6903-2RS) that fits perfectly into the impeller shaft housing and almost fits the shaft too.
The shaft needed a bit of grinding to fit into the bearing. Once fitted i cut a groove on the shaft in order to use a circlip to secure the bearings in place.
I cut a small piece of the old bearing to use as spacer and assembled both bearings. I marked the groove for the second circlip and cut it.
Finally i made a spacer ring out of a bicycle spoke to prevent the bearing from coming into contact with the oil seal.