Hello @pratched
Sorry for my late reply. In the meantime, support has responded to my request regarding the rear module.
Unfortunately, they refused to send me this replacement part. I would have to send my entire phone to the repair center.
This goes against Fairphone’s whole philosophy regarding self-repair if they won’t provide you with something as simple as this plastic frame.
But yesterday I replaced my broken rear module with the one from the water damaged Fairphone 3 - aaaand oh wonder - my GPS works again 
Also my cell phone reception seems to be a bit better - although I never really noticed that before 