Italjet Drasgster rear wheel play

Hello seem to have a problem with my Italjet Dragster.

I seem to be getting a lot of play in the rear wheel. Originally is was the axle bolt coming loose but I have now put on the tsab locking ring which has stopped the bolt working loose.

However now the bolt is staying tight but after a short ride the play still comes back the previous owner did run an extra washer in the hub which I took out but I believe it should only have one in there ?

Once I have tightened it all up the play does disappear but then comes back could it possibly be a worn hub but I thought if it was this the play would be permanent even when tight ?

Any one got any ideas ??

 

Have you changed the gearbox bearing on the output shaft?