Dishwasher not cleaning. I have a HELLER DWH3 dishwasher and the top washing arm is not spinning

Question

I have a HELLER DWH3 dishwasher and the top washing arm is not spinning around. The detergent is just staying in the place where it goes. The water pressure is awesome and i have taken the whole tray out to see if there is a blockage there but there isn't. It is a plastic arm. It is quite wobbly but it spins freely by hand and has only just started doing this so my dihes are not cleaning! I am in New Zealand.