AEG refrigerator freezing problem

Hi I was on here a few months ago when my AEG 4085-8KG started freezing everything in the refrigerator compartment. Many thanks to all for help finding parts diagram. Fiddling with connectors seemed to make the problem go away but now its back with a vengeance!
I swapped the main PCB and the probe (Number 129 in attached diagram) but to no effect. There is another probe in the refrigerator compartment (number 128) but as it is located behind the flat metal cooling plate, I am struggling to know how to get to it?
The metal plate appears to be secured by strips of triangular plastic beading down either side. Can I remove this or will I risk puncturing a refrigerant pipe?