I'm going to take a wild guess and say that it is the light sensitive diode for the light metering.
It sounds like they took the name of the part in German and translated it directly into Engish, but technical terms are unfortunately all too often quite different in different languages and completely non-obvious even if you speak them well.
The only thing in a M6 that I can think of that would be Empfänger (Receiver in German) would be the diode - the lens mount is Bajonett, the film take up spool is Spule or Filmspule, hot shoe Blitzschuh, and I think there would have to be a terrible mistake to have these come out as receiver in English.
My German is terrible, so I could be completely wrong 😉
When I first moved here, with even worse German than I have now, I had a similar trouble trying to find out how to ask for push processing. Was it simply push in German? Of course even people who spoke perfect English and German had no idea because they didn't even no what it was. In the end I went to a pro lab because I thought at least they would be able to guess what I was asking for even if the word was wrong. I ended up paying nearly 30 euros for developing and printing 6" by 4" on a completely normal processing machine.
It turned out that the word for push developing in German is the English word 'Push'.