Just a quick note, and I know this is an old thread... while searching for the fix I found this, and wanted to add my own notes, just in case they are useful to others.
I just bought a KR10 Super - had one when I was 13
Shutter was stuck. I could release it by turning the motor drive interface on the base plate anti-clockwise. There was a quiet click, and away it went again.
I did however send the camera away for a full service including light seals, and now it's perfect of course. Pretty much dried up grease/oil.
As of Nov 2023, this cost roughly £80 including the new seals, a cost that I thought was well worth it.