Good thing we got accepted for a Sugru Build Night. So, how do you fix that switch with Sugru? It's way too small just to glue it using Sugru. The part itself should be bigger to have more surface touching Sugru, and whe would have the problem of accessibility inside the case again.
So i decided, I'd leave out the plastic part that broke away, and just fixate the plastic swith upon the technical switch. On this way, the switch will stay in position, and since I don't think I'll have to seperate that part ever again, I could totally do that.
So i took a small ball of Sugru, put it to the place where the plastic part would touch the switch, put it into place and fixated the front panel, so it won't move while drying. As simple as that.
I have not been too accurate, so you can see a small amount of the Sugru from the front panel (I applied it too thickly), but it works and stays perfectly in place. The feeling of the switch changed a bit, because the distance became a bit higher, but that's really not a problem here.
Anyways, this amplifier is meant to be placed at our elecricity workbench, so appearance is not an issue.
On this way, I got a donated amlifier to work again, and we now can listen to music while soldering. Great! :)