Yes, it is down to quality. Leica used ball bearings and well machined bushings whereas the Russian copies do not. These copies also used poor quality lubricants which separate into grease and oil. All this causes wear and increases friction, making shutter fade more likely. Often people try to compensate by over tensioning the opening curtain, or both curtains to overcome the friction. This just increases the wear. I'm just trying to fit new curtains to a Zorki 3M (wish I'd never started) - the wear on the bearing surfaces is clear to see. The problem with the 'new old stock' curtains is that they have stiffened and do not want to wind around the drums, making this a nightmare job. Think I'll stick with my Contax II !!