Hey, sorry for my lousy reply. I'm a bit busy at the moment. Repair Manual scan and viewfinder "service" instruction will follow in mid-end december. Sorry for that, but that takes some time. Wanna do it thoroughly. But it will come in a separate post. I'll inform you here.
I nevertheless have a question to my problem: I did disassemble the whole shutter in order to get to my problem (I consider writing an instruction with pictures here as well because I did not find anything on the internet, so someone will most likely find that useful). It sees that a screw on the back is the problem (see attached picture, 12 o'clock on the ring, its the slotted screw). When I press the release everything runs very slow, mostly halts completly. I assumed oily blades etc., which is why I disassembled it completly and cleaned every blade with isopropyl alcohol. I even removed the guide ring and cleaned that. Reassembled everything: same behaviour. I noticed that when I release the aforementioned screw that suddenly I runs as intended. The screw, however, is now not really tighented, rather loose. This is most likely not intended. A friend of mine suggested that a washer is missing. However, when disassembling I did not find a washer at all. Also, the problem was already before disassembling the shutter at all. Does someone have an idea what I am missing? Just leaving out a screw feels very very wrong.
Looking forward to your answers.
Best