I ran the test as suggested and cleaned out the upper and ower arms. Unfortunately it did not make any improvement.
However, what I did notice was that when the spray arms were off and with the machine started, when I opened the door during the cycle the water was being pumped through the inlet at the bottom of the machine. Would this indicate that the motor is working as expected?
I have noticed that there is a lot of up and down movement in the lower spray arm when I put it back and wondered if it was worn, thus allowing the pressurised water to leak before it gets into the lower spray arms and the pipe work to the upper arm.
Should there be any play in the dpray arms, and I coud not see any evidence of washers or seals, is this standard?