Thanks for sharing your experience with repairing the microphone @unhawkable! I had almost missed this post of yours since the thread is about repairing the µUSB port, perhaps one of the kind mods could split the topic and title it appropriately? 
I’m currently facing a similar issue with the microphone not working while the rest of the bottom module continues to function. I’m hoping it’s not the traces on the board that have cracked, that it’s only the solder on the surface mount that has cracked which can be fixed by melting it with the heat gun and letting it cool again, doing a reflow of sorts.
Are there any gotchas I should be aware of before attempting this? I assume it’s better to loosen the glue with the heat gun and remove the board from the plastic casing to avoid melting it. Did you heat up the whole board or just the area around the microphone? What temperature did you heat it up to, did it not damage the mic? (I would’ve assumed excessive heat would’ve damaged the coil found in a dynamic mic, but the FP2 may be using a piezo mic or even something completely different; is the type of mic used here known?)
I’ll be sure to report back with the results. In the (fairly likely) case that I fail, I’m already looking around for a replacement module anyway - the only reason I’m even attempting this is because they’re no longer available from the web shop.