Just a few days ago I discovered the dial-set Compur shutter on a very nice old lens (Xenar typ D 15cm f:3,5) would only fire at 1/200 - regardless of setting. A quick google search gave me a page with basic dismantling instructions, so I dug out my screwdrivers and got to work.

One hour, four Q-tips, two drops of fine oil (valve oil for brass instruments) and some drops of lighter fuel later the shutter was operating correctly again - and all times were less than 10% off.

They are quite simple, yet ingenious shutters. I will always try the repair myself before sending a shutter for surgery: Either I can fix it for free, or it will be expensive anyway.

BTW, the 150/3,5 shutter is another one of the non-standard threaded ones, so replacement is not an option.