Thanks again. The volume buttons (1), the tiny coax(?) connector (4) and the screen(?) connectors (5) were not an issue at all. The most challenging bit was persuading the front camera (2, the black rectangle, you refer to it as proximity sensor) to come out. It was not only a tight fit but also fixed with a sticky pad. And of course the two flex connectors (3). The end of the top one was glued to the metal shielding with some sticky substance and I was a bit worried, but it came off quite easily.

In the end, I made things even worse. I got to the earpiece and it looked clean, but I could not take it out and could only see its back. So I merely pushed the spring contacts up a bit to make a better contact. That may have been a mistake because the sound is even more distorted than before. Perhaps the springs push on the speaker too much and the membrane is squashed. Which actually gives me some hope. The distortion sounds exactly like before, only stronger, which means the reason was possibly some dross pushing the membrane. I can try to take it apart again and have a closer look, but it may take another day or two. If I fail again, I will take up your kind offer.