Have you had the camera long?
If not, it may be that the previous owner did not use it much.
Before you send it off for repair, it is worth firing at every shutter speed at least 10 times per day for several days. Then run another test roll. If the problem is cured or partly cured then thye problem lies in lack of use and regular firing throughout the shutter speed range will be something you need to do on a regular basis. If it does not help then you will need a CLA by a qualified Leica repairer.
In my case, exercising the shutter did work for me when I bought a Leica many years ago from a collector who had it for a long time purely for display.
Bests,
David
www.dsallen.de