After developing my negatives from our Tokyo trip, I noticed a thin band of overexposure on a few frames I shot over 1/125, as seen in the two pictures above. Eventually, I also lost speeds below 1/60. These were indications that the curtain drum and rollers where dirty, dry or both.
So I downloaded and studied the service manual. This manual is just a reverse engineering illustration of how the camera was built. There are no instructions on how to service the camera.
Even if I've had previous experience restoring a Leica II and a few Feds and Zorkis, I ruled out dismantling the shutter mechanism on this more complex camera. I didn't even consider adjusting the shutter tension. My main objective was to gain access to the curtain drum and rollers which were blocked by light baffles so I could flush them with Naptha and then re-lubricate. After this procedure, 1/125-1/1000 looked much better on the CRT screen shutter test. I loaded a test roll.
Test shots after DIY/CLA