Complex sentence: Apparently one key issue is the rough finish on the gears of the internal mechanisms, causing the film advance to become stiff and sound like "grinding walnuts" according to some accounts.
Split into simpler sentences: Apparently one key issue is the rough finish on the gears of the internal mechanisms. If not individually polished, then winding on the film will eventually become stiff and sound like "grinding walnuts" according to some accounts.