The SF7s I've noticed this on are at least twenty years old already. I see no reason for them to break down unless mistreated.

The later MZ-series bodies however appear to be the proverbial time bomb. There's a tiny plastic drive cog on a motor near the lens mount (below and to the right as you hold the camera normally). As is common with many small plastic cogs it was moulded a bit too small for the motor shaft, so it eventually splits. You can buy a replacement motor with a metal cog but it looks seriously fiddly to install.