AEG Favorit 40650

My AEG Favorit 40650 PWC 91123263601 is leaking water from the overflow pipe at the bottom of the water regenerator cassette on the fill cycle.
I had this problem before and last time cleaning the hinge from the cassette cured it. So I removed and cleaned as much of the grunge as possible and replaced it – however this time it made the problem worse. It now leaks about 0.5l on each fill or about 1.5l over a normal cycle.
I have the side off and the pipe draining into a bowl so that the anti flood switch is not triggered and the machine otherwise works perfectly.
I have read all the advice I can find and I am still flummoxed. The cassette remains my chief suspect but it’s a lot of water to be explained by a blockage in there.
I haven’t checked the pressure switch or the inlet valve but seems to me that if either of these was faulty it would just keep filling since I’ve bypassed the anti flood system. This machine does not have a float chamber but has a reed switch instead could this be faulty?
Advice would be really welcome.
Nb if I do need to multimeter the inlet valve do I need to put it across the terminals on the inlet valve or the solenoid itself which is mounted away from the valve in this nachine.