About Shutter Speeds
You hear/read a lot of things about shutter speeds of old leaf shutters that I have found not to be true. For instance:
Shutter speeds are erratic. In my experience a leaf shutter in good condition is consistent, varying less than 1/6th of a stop for a given setting (overall not plus/minus). Accuracy of marked speed is not as close because they were adjusted by the factory to specified tolerances which were not as tight, but usually are within plus/minus 1/3 stop. A careful tech can do much better.
High speeds are slow. This seems to be a result of incorrect measurements. Shutter efficiency has to be taken into account. Using my Calumet Shutter Speed Tester according to instructions my shutter is actually slightly fast (1/500 rather than the marked 1/400), if I do not follow the instructions I get a reading of about 1/250 second. You can easily approximate this by adding 2 milliseconds (.002) to the shutter tester reading, and save the trouble of getting a dimer for the light source. That will be close enough to the true speed to tell if the shutter is working properly.
The above were true of my current, apparently pre-war, Graphex shutter after cleaning and lubing according to the instructions here on my site. It was also true for the shutter in a 100/2.8 lens on a Mamiya Universal, a Rolleiflex Compur in a 80/2.8 Xenotar, both a Xenar 150/4.5 and an Angulon 90/6.8 in Compur shutters for a Linhof Super Technica III. None of these needed any sort of adjustment, just a thorough cleaning and lubrication.
If a shutter is not within the above kinds of tolerance, or it is hard to change the shutter speeds (except to the one or two highest speeds which often have a booster spring that cocks when you do so), or shows any kind of hesitation it needs servicing. If you have good mechanical skills, and work very carefully you can do it yourself. My experience, is it takes about 4 hours to completely tear down, clean, lube, and reassemble a shutter of a type I have never worked on before, and about 2 hours to do one that I am familiar with.
Since we are mostly talking about old shutters here, if it has problems beyond those mentioned in the previous paragraph something is probably broken and it probably needs repair as well. In that case I would suggest sending it off to someone who specializes in this sort of repair and has a source of parts available (probably from junk shutters).
I do not recommend just rinsing the shutter in solvent as that removes the lubricants, but not the grit and does nothing to clean out any corrosion. Soaking in solvent can also dissolve, or at least soften, paper insulators that were used in the sync circuits of many old shutters. And for sure, you do not want to flood the shutter in oil.