Citronic dimension 4 power amplifier switch not working in stereo

Hi all, firstly any guidance and information will be much appreciated

I have a dimension 4 amplifier that I just bought.

It is in 'as new' condition except the switch on the front only works in both channels in mono, when I switch it to stereo it only works in one channel and the other channel is dead.

I actually prefer to use this amp in mono yet still want the unit working fully as it's in great condition.

So far I have:
Used contact cleaner in the switch

Reflowed the switches and preamp boards solder joints as it's the terrible lead free solder which is the worst solder I've seen, really just bubbles and pops

Tried both jack and XLR inputs and checked the buttons on the back are not in bridge mode or anything

My question is, is the switch faulty or could it be another issue? I've not come across an issue like this before
 
I removed the board with the switch on.

I checked for continuity and had continuity between two pins with the switch out (mono) and only continuity between one pin with the switch in (stereo).

As the switch was easier to get a good clean with contact cleaner with the switch board out I sprayed it again well.

Allowed it to dry, checked for continuity and all is well, fired it up and its now fully working.

Thanks for your help. I'm not experienced with switch problems yet learning well.
 

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