Hi,
I also want to share my experience with repairing the microphone.
From one day to the next my microphone didn’t want to work anymore. This was not the first time but now, I can’t buy a new bottom module…
I read a few times that the pcb tracks are maybe cracked. So I opend my bottom module, heated it up to soften the glue and the solder and removed the microphone from the pcb. And the result was: All three tracks are broken (now) 
(see picture below)…
The solderpads of the pcb were still on the bottom side of the microphone. And as you can see, there is a short between two of the four contacts. After cleaning up and solder removing, you can see in the green pcb of the microphone, there is already a short between these two contacts. Therefore, the microphone need only 3 contacts to the board.
I scratched away the black of the three remaining tracks so that you can see the copper and you have new contactpads for soldering. The microphone contacts got new solder (a little bit too much) und flux so that there is enough which can flow to the new contactpads. I put the microphone back on the pcb, a little bit displaced so that the solder is over the new pads, heated it up and pressed it to the board.
And now, it works again! 
(I hope you can see the picture. It is the first time for me to post a picture.
Also, I’m sorry for the bad quality. I took the picture with my FP2 through the ocular of a normal microscope 
)