I’ve repaired a non-working bottom module. The microphone didn’t work at all. But I could make it work by pressing firmly the bottom right.
I’ve opened the module (using a torx #5 for the 2 screws). The golden contact plate was slightly curved. I slided a cardboard underneath (as shown on the picture). I also put a piece of cardboard between the screen and the bottom module in line with the contacts.
The microphone is working again. I guess that the contact pins distort the plate after a while.
Hope it helps.