Excess rinse aid use?

The machine is a Beko 5412. It is using far more rinse aid that it used to, despite the control being turned down to minimum.
I have had the dispenser out and cleaned it up and suspect the issue is down to the rubber valve (which would probably cost a quid to replace but I bet I can only buy the whole dispenser!).
The question is this: When the solenoid operates, the spring loaded arm in the middle moves to the left and operates the valve, then on the next operation, moves back to the right without operating the valve. So where should it be at the beginning of the wash cycle?

Iain
November 2020